JavaScript objects in examples. Fundamental JavaScript Objects

Objects are the cornerstone of JavaScript. Many built-in data types are represented as objects. To be a successful JavaScript developer, you need to have a clear understanding of how they work. The building blocks of an object are called its fields or JavaScript object properties. They are used to describe any aspect of an object. The property could describe the length of a list, the color of the sky, or a person's date of birth. Creating objects is an easy process. The language provides a syntax known as object literals, which are denoted by curly braces.

Accessing Properties

The language provides two entries for accessing properties. The first and most common is known as dot notation. In dot notation, a resource can be accessed by specifying the name of the host object, followed by the period and the name of the property. For example, when object.foo was initially set to one, then its value will become 2 after the JavaScript objects statement is executed.

An alternative access syntax is known as bracket notation. In notation, the object name is followed by a set of square brackets. In them, the property name is specified as a string:

object["foo"] = object["foo"] + 1.

It is more expressive than dot notation because it allows a variable to specify all or part of a property name. This is possible because the JavaScript object interpreter automatically converts this expression to a string and then obtains the corresponding property. Property names are created on the fly by concatenating the contents of the variable f with the string "oo":

object = "bar".

Bracket notation allows property names to contain characters that are prohibited in dot notation. For example, the following statement is completely legal in parentheses. However, if the user tries to create the same property name in dot notation, they will encounter a syntax error:

object["!@#$% &*()."] = true.

Properties of nested JavaScript objects can be accessed by chaining dots and/or parentheses. For example, the following object contains a nested object named baz that contains another object named foo that has a property named bar containing the value five:

var object = ( baz: ( foo: ( bar: 5 ) ) ).

The following expressions access the bar attached property. The first expression uses dot notation, while the second expression uses square notation. The third expression combines both entries to achieve the same result:

object.baz.foo.bar;
object["baz"]["foo"]["bar"];
object["baz"].foo["bar"].

Expressions like those shown in the previous example can cause performance degradation if used incorrectly and cause the JavaScript object to fail. Evaluating each dot or bracket expression takes time. If the same property is used multiple times, then it makes sense to access the property once and then store the value in a local variable for all future uses.

Function as method

When a function is used as a property of an object, it is called a method. Like properties, they are specified in object literal notation. For example:

var object = ( sum: function(foo, bar) ( return foo + bar; ) ).

JavaScript object methods can be called using marks and parentheses. The following example calls the sum() method from the previous example using both entries:

object.sum(1, 2);
object["sum"](1, 2).

Object literal notation is useful for creating new objects, but it cannot add properties or methods to existing ones. Luckily, adding new data is as easy as creating an assignment statement. An empty object is created. Then, using assignment operators, we add two properties, foo, and bar, and the baz method:

var object = ();
object.foo = 1;
object.bar = null;
object.baz = function() ( return "hello from baz()"; ).

Program Encapsulation

The basic idea of object-oriented programming is to divide programs into smaller parts and make each part responsible for managing its own state. Thus, some knowledge about how a part of a program works may be local to that part. Someone working on the rest of the program shouldn't remember or even know about it. Whenever this local data changes, only the code immediately around it needs to be updated.

The various parts of such a program interact with each other through interfaces, limited sets functions or bindings that provide useful functionality at a more abstract level while hiding their exact implementation. Such parts of a program are modeled using objects. Their interface consists of a specific set of methods and properties. Properties that are part of an interface are called public. The rest, which should not touch external code, are called private.

Many languages provide the ability to distinguish between public and private properties and do not allow external code to access private ones. JavaScript, again taking a minimalist approach, is not there yet. Work is currently underway to add this language. Therefore, JavaScript programmers will successfully use this idea. Usually, accessible interface described in the documentation or comments. It is also common practice to place an underscore (_) at the beginning of property names to indicate that the properties are private. Separating the interface from the implementation is a great idea. This is usually called encapsulation.

Properties

An object with parentheses (...) is called an object literal. You can immediately place some properties in such brackets (...). For example, pairs “key: value and so on”:

let user = ( // an object name: "John", // by key "name" store value "John" age: 30 // by key "age" store value 30 }.!}

A property has a key (also known as a "name" or "identifier") before a colon ":" and a value to the right of it. The user object has two properties. The resulting JavaScript user object with two signed files labeled "name" and "age". You can add, delete and read files from it at any time. Property values are accessed using dot notation. It can be of any type. You can add a boolean value. To remove a property, use delete in case Error object and JavaScript.

All JavaScript error objects are descendants of the Error object or an inherited object:

The Syntax Error object inherits from the Error object.

JSON Parse error of a certain type of Syntax Error object.

To take an even deeper dive into understanding how applications deal with JavaScript errors, take a closer look at Airbrake JavaScript, an error tracking tool for real-time alerts and instant insight into what went wrong with your JavaScript code.

Error messages that a user may receive before deleting a JavaScript object:

Bad control character in a string literal.

Bad character in a string literal.

Poor Unicode output.

Bad escape character.

Unterminated string.

Unexpected non-numeric code.

There are no numbers after the decimal point.

Unterminated fractional number.

There are no numbers after the degree indicator.

There are no numbers after the exponent sign.

The exponential part has no number.

Unexpected end of data.

Unexpected keyword.

An unexpected symbol.

End of data when reading the contents of an object.

Expected property name or ")".

Computational properties

You can use square brackets in an object literal. These are called computed properties. An example is given below.

The meaning of a computed property is simple: it means that the property name must be taken from fruit. So if a visitor enters "apple", bag will become (apple: 5). You can use more complex expressions in square brackets:

let fruit = "apple";

: 5 // bag.appleComputers = 5

Square brackets are much more powerful than dot notation. They allow property names and variables. But they are also more cumbersome to write. So most of the time, when property names are known and simple, a dot is used. And if you need something more complex, then switch to square brackets.

Word reservation

A variable cannot have a name equal to one of the reserved words such as "for", "let", "return", etc. But when sorting JavaScript objects, there is no such restriction.

In principle, any name is allowed, but there is a special one: it "__proto__" gets special treatment for historical reasons. For example, you cannot set it to a value other than an object:

obj.__proto__ = 5;

alert(obj.__proto__); // didn't work as intended

As you can see from the code, the purpose of primitive 5 is ignored. This can be a source of errors and even vulnerabilities if the operator intends to store arbitrary key-value pairs in an object and allow the visitor to specify the keys. In this case, the visitor can select "proto" as the key and add JavaScript to the object. There is a way to make objects treated with __proto__ as a regular property. There is also another map of data structures that support arbitrary keys.

Integer Properties

The term "integer property" here means a string that can be converted from an integer without modification. So, for example, "49" is an integer property name because when it is converted to an integer and back again, it is still the same. But “+49” and “1.2” are not like that. On the other hand, if the keys are not integer, then they are listed in the order they were created. Example below.

To fix the problem with dialing codes, you can "cheat" by making the codes incomplete. Adding a "+" (plus sign) before each code is sufficient. Now it will work as intended.

The difference between objects and primitives is that they are stored and copied “by reference”. Primitive values are assigned and copied "as an integer value". A variable stores an "address in memory" rather than the object itself or a "reference" to it. You can use any variable to access and change its contents.

The example above shows that there is only one object and admin to log into it. Then, if a different key (user) is later used, the user will notice the changes.

The equality operators == and strict equality === for objects work the same way. Two objects are equal only if they are the same object. For comparisons like obj1 > obj2 or comparisons with the primitive obj == 5, the objects are converted to primitives. To be honest, such comparisons are very rarely needed and are usually the result of a coding error.

JavaScript Object Validation

Objects have access to any property. However, if it doesn't exist at all, it won't be an error. Only accessing a non-existent property returns undefined. It provides a very common way to test a property and compare it to an undefined one. Below is an example.

Using "in" for properties that store undefined. Usually a strict "=== undefined" comparison check works fine. There is a special case where it fails and "in" works correctly. This is when a property of an object exists but remains undefined.

In the code above, the obj.test property technically exists. Therefore the in operator works correctly. Similar situations happen very rarely because undefined is not usually assigned. Mostly null "unknown" or "empty" values are used. Thus, the in operator is effectively a guest in the code.

"for..in" loop

In order to move through all the keys from object to object, there is a special form of loop: for..in. This is a completely different thing from the for(;;) construct.

Below is an example.

Please note that all “for” constructors allow you to declare a looping variable inside a loop as a let key. Alternatively, you can use a different variable name, key, instead.

For example, for(let prop in obj) is also widely used.

There is an alternative "square bracket" that works with any string.

The point here requires that the JavaScript object's keys be a valid variable identifier, meaning there are no spaces or other restrictions. Care must be taken to ensure that the line inside the brackets is quoted correctly. Square brackets also provide a way to get the property name from the result of any expression, as opposed to a literal string from a variable:

let key = "likes birds";

// same as user["likes birds"] = true;

user = true.

Here the key variable can be calculated at runtime and depends on user input and then used to access the property. This gives programmers more flexibility. Dot notation cannot be used in a similar way, as it would iterate over the JavaScript object. Below is an example.

Const object

A declared const object can be modified. An example is given below.

It might seem like the JavaScript object in line (*) would throw an error, but that's not the case. This is because const captures the value of user itself. And here the user keeps a reference to the same object all the time. The line (*) goes inside the object, it is not reassigned to user. Const will give an error if you try to set user and something else. Cloning and merging, Object.assign creates another reference to the same object if it needs to be duplicated. This is also doable, but a little more difficult because JavaScript doesn't have a built-in method. In fact, this is rarely necessary. Copying by reference is used in most cases. But if you really need this, then you need to create a JavaScript object and replicate the structure of an existing one, copying its properties at a primitive level. Below is an example.

And you can also use the Object.assign method for this. The arguments dest and src1, ..., srcN are objects. It copies the properties of all objects src1, ..., srcNINTO dest. In other words, the properties of all arguments, starting from the second, are copied to the 1st. Then it returns to dest. For example, you can use it to combine several objects into one.

And you can also use Object.assign to replace the simple cloning loop. It copies all of the user's properties to an empty object and returns it, just like a loop, but shorter. Until now, it has been assumed that all user properties are primitive. But properties can be references to other objects.

To fix this, you need to use a clone loop that checks each user value and, if it is an object, then replicates its structure. This is called "deep cloning."

There is a standard deep cloning algorithm that handles the above case and more complex cases called the Structured cloning algorithm. To avoid reinventing the wheel, you can use a working implementation from the lodash JavaScript library, the method is called _.cloneDeep(obj).

Advanced Methods

If a programmer loops over an object and wants to get all the properties in the same order they were added, he can rely on "special ordering," where integer properties are sorted and others are formed in the order in which the JavaScript object was created.

Advanced object methods deal with concepts that are rarely used in JavaScripting. This is because in normal scenarios these powerful features are not needed. Some of these methods may not work in older browsers, such as early releases of Netscape 4.

The prototype could be used to create JavaScript objects and all mycircle methods, not just the new ones. This has a mixed performance impact. They shouldn't store individual copies methods for each object instance, so may require less memory to operate, but the browser must look for the current and parent scopes to find them. This may result in extreme latency. Generally, the user should use what is appropriate for the code rather than basing that decision on performance, unless they are dealing with a very specific controlled environment.

Return true

In some cases, it may be necessary for an object's property to be bound to the object itself or somewhere in the prototype chain. In JavaScript, all objects use the hasOwnProperty method, which returns true if that property is bound to an individual object instance. In this case, it becomes possible to check whether the constructor of an object has the same property with the same value as the object instance itself. This may give incorrect results if there are separate JavaScript object properties with the same value for both the object instance and the circuit prototype. The hasOwnProperty method takes a single parameter - the property name as a string.

You can create private methods in a similar way. It is simply a function that is created inside a constructor function. This may seem confusing to some, but that's how it works. A private function can only be called by the constructor itself or by methods that are defined on the line. They can be used as public methods if assigned to a public constructor and accessed using public methods of Javascript objects.

function myob() ( function cantBeSeen() ( alert(secretValue);

) var secretValue = "";

this.method1 = function () ( secretValue = "no surprises";!}

this.method2 = cantBeSeen;

) var oneOb = new myob();

oneOb.method1();

//alerts "no surprises" oneOb.method2();

//alerts "no surprises".

Command Template

Command objects allow for loosely coupled systems by separating those that issue a request from objects and those that actually process the request. These requests are called events, and the code that processes the requests is called event handlers.

Suppose you are creating applications that support the clipboard actions Cut, Copy and Paste. These actions can be triggered in different ways throughout the application: by the menu system, context menu, for example, by right-clicking a text field or using a keyboard shortcut. Command objects allow you to centralize the processing of these actions, one for each operation, when only one command is needed to process all Cut requests, one for all Copy requests, and one for all Paste requests.

Because teams centralize all processing, they are also often involved in handling undo functions for the entire application. Significant improvements can be achieved by applying modern JavaScript techniques, resulting in more efficient, reliable, and maintainable applications.

To learn how to do this, you can use JavaScript + jQuery templates. This unique package includes optimized JavaScript for all GoF templates using more advanced features such as namespaces, prototypes, modules, function objects, closures, anonymous functions and more. If users need latest tools and methods for JavaScript templates, jQuery templates and template architectures then this the best option use. This package contains valuable, up-to-date information For JavaScript developers. Here's what's included:

JavaScript-optimized GoF templates.

Modern JavaScript Design Patterns.

Model-View Design Patterns.

jQuery Design Templates.

Architectural patterns of JavaScript idioms.

Example applications (MVC, SPA, etc.)

The proposed basics of JavaScript object syntax are very important for beginning programmers. One must first understand objects, then there will be knowledge of object-oriented programming. It is critical to have a deep understanding of this material as it serves as the foundation for the rest of the JavaScript language.

JavaScript is designed on a simple object-based paradigm. An object is a collection of properties, and a property is an association between a name (or key) and a value. A property"s value can be a function, in which case the property is known as a method. In addition to objects that are predefined in the browser, you can define your own objects. This chapter describes how to use objects, properties, functions, and methods, and how to create your own objects.

Objects overview

Objects in JavaScript, just as in many other programming languages, can be compared to objects in real life. The concept of objects in JavaScript can be understood with real life, tangible objects.

In JavaScript, an object is a standalone entity, with properties and type. Compare it with a cup, for example. A cup is an object, with properties. A cup has a color, a design, weight, a material it is made of, etc. The same way, JavaScript objects can have properties, which define their characteristics.

Objects and properties

A JavaScript object has properties associated with it. A property of an object can be explained as a variable that is attached to the object. Object properties are basically the same as ordinary JavaScript variables, except for the attachment to objects. The properties of an object define the characteristics of the object. You access the properties of an object with a simple dot-notation:

ObjectName.propertyName

Like all JavaScript variables, both the object name (which could be a normal variable) and property name are case sensitive. You can define a property by assigning it a value. For example, let"s create an object named myCar and give it properties named make , model , and year as follows:

Var myCar = new Object(); myCar.make = "Ford"; myCar.model = "Mustang"; myCar.year = 1969; myCar.color; // undefined

Properties of JavaScript objects can also be accessed or set using a bracket notation (for more details see property accessors). Objects are sometimes called associative arrays, since each property is associated with a string value that can be used to access it. So, for example, you could access the properties of the myCar object as follows:

MyCar["make"] = "Ford"; myCar["model"] = "Mustang"; myCar["year"] = 1969;

An object property name can be any valid JavaScript string, or anything that can be converted to a string, including the empty string. However, any property name that is not a valid JavaScript identifier (for example, a property name that has a space or a hyphen, or that starts with a number) can only be accessed using the square bracket notation. This notation is also very useful when property names are to be dynamically determined (when the property name is not determined until runtime). Examples are as follows:

// four variables are created and assigned in a single go, // separated by commas var myObj = new Object(), str = "myString", rand = Math.random(), obj = new Object(); myObj.type = "Dot syntax"; myObj["date created"] = "String with space"; myObj = "String value"; myObj = "Random Number"; myObj = "Object"; myObj[""] = "Even an empty string"; console.log(myObj);

Please note that all keys in the square bracket notation are converted to string unless they"re Symbols, since JavaScript object property names (keys) can only be strings or Symbols (at some point, private names will also be added as the class fields proposal progresses, but you won't use them with form). For example, in the above code, when the key obj is added to the myObj , JavaScript will call the obj.toString() method, and use this result string as the new key.

You can also access properties by using a string value that is stored in a variable:

Var propertyName = "make"; myCar = "Ford"; propertyName = "model"; myCar = "Mustang";

Using a constructor function

Alternatively, you can create an object with these two steps:

Define the object type by writing a constructor function. There is a strong convention, with good reason, to use a capital initial letter.

Create an instance of the object with new .

To define an object type, create a function for the object type that specifies its name, properties, and methods. For example, suppose you want to create an object type for cars. You want this type of object to be called Car , and you want it to have properties for make, model, and year. To do this, you would write the following function:

Function Car(make, model, year) ( this.make = make; this.model = model; this.year = year; )

Notice the use of this to assign values to the object"s properties based on the values passed to the function.

Now you can create an object called mycar as follows:

Var mycar = new Car("Eagle", "Talon TSi", 1993);

This statement creates mycar and assigns it the specified values for its properties. Then the value of mycar.make is the string "Eagle", mycar.year is the integer 1993, and so on.

You can create any number of Car objects by calls to new . For example,

Var kenscar = new Car("Nissan", "300ZX", 1992); var vpgscar = new Car("Mazda", "Miata", 1990);

An object can have a property that is itself another object. For example, suppose you define an object called person as follows:

Function Person(name, age, sex) ( this.name = name; this.age = age; this.sex = sex; )

and then instantiate two new person objects as follows:

Var rand = new Person("Rand McKinnon", 33, "M"); var ken = new Person("Ken Jones", 39, "M");

Then, you can rewrite the definition of Car to include an owner property that takes a person object, as follows:

Function Car(make, model, year, owner) ( this.make = make; this.model = model; this.year = year; this.owner = owner; )

To instantiate the new objects, you then use the following:

Var car1 = new Car("Eagle", "Talon TSi", 1993, rand); var car2 = new Car("Nissan", "300ZX", 1992, ken);

Notice that instead of passing a literal string or integer value when creating the new objects, the above statements pass the objects rand and ken as the arguments for the owners. Then if you want to find out the name of the owner of car2, you can access the following property:

Car2.owner.name

Note that you can always add a property to a previously defined object. For example, the statement

Car1.color = "black";

adds a property color to car1, and assigns it a value of "black." However, this does not affect any other objects. To add the new property to all objects of the same type, you have to add the property to the definition of the Car object type.

Using the Object.create method See also

To dive deeper, read about the details of javaScript's objects model.
To learn about ECMAScript 2015 classes (a new way to create objects), read the JavaScript classes chapter.

Last update: 04/08/2018

Object-oriented programming is one of the dominant paradigms in application development today, and in JavaScript we can also take full advantage of OOP. At the same time, in relation to JavaScript, object-oriented programming has some features.

Objects

In previous topics, we worked with primitive data - numbers, strings, but data does not always represent primitive types. For example, if in our program we need to describe the essence of a person who has a name, age, gender, and so on, then naturally we will not be able to represent the essence of a person as a number or string. We will need a few lines or numbers to properly describe the person. In this regard, a person will act as a complex complex structure, which will have individual properties - age, height, first name, last name, etc.

To work with such structures, JavaScript uses . Each object can store properties that describe its state and methods that describe its behavior

Creating a new object

There are several ways to create a new object.

The first way is to use the Object constructor:

Var user = new Object();

In this case, the object is called user. It is defined in the same way as any regular variable using the var keyword.

The new Object() expression represents a call to a constructor, a function that creates a new object. The new operator is used to call a constructor. Calling a constructor is essentially like calling a regular function.

The second way to create an object is by using curly braces:

Var user = ();

Today, the second method is more common.

Object properties

After creating an object, we can define properties on it. To define a property, you need to specify the name of the property after the name of the object, separated by a dot, and assign a value to it:

Var user = (); user.name = "Tom"; user.age = 26;

In this case, two properties name and age are declared and assigned corresponding values. After that, we can use these properties, for example, display their values in the console:

Console.log(user.name); console.log(user.age);

You can also define properties when defining an object:

Var user = ( name: "Tom", age: 26 );

In this case, a colon character is used to assign a value to the property, and a comma (rather than a semicolon) is placed after the property definition.

In addition, there is a shortcut way to define properties:

Var name = "Tom"; var age = 34; var user = (name, age); console.log(user.name); // Tom console.log(user.age); // 34

In this case, the names of the variables are also the names of the properties of the object. And this way you can create more complex designs:

Var name = "Tom"; var age = 34; var user = (name, age); var teacher = (user, course: "JavaScript"); console.log(teacher.user); // (name: "Tom", age: 34) console.log(teacher.course); // JavaScript

Object Methods

An object's methods define its behavior, or the actions it performs. Methods are functions. For example, let's define a method that would display a person's name and age:

Var user = (); user.name = "Tom"; user.age = 26; user.display = function())( console.log(user.name); console.log(user.age); ); // calling the method user.display();

As with functions, methods are first defined and then called.

Methods can also be defined directly when defining an object:

Var user = ( name: "Tom", age: 26, display: function())( console.log(this.name); console.log(this.age); ) );

As with properties, a method is assigned a function reference using a colon.

To access properties or methods of an object within that object, use the this keyword. It means a reference to the current object.

You can also use a shorthand way to define methods by omitting the colon and function:

Var user = ( name: "Tom", age: 26, display())( console.log(this.name, this.age); ), move(place)( console.log(this.name, "goes to" , place); user.display(); // Tom 26 user.move("the shop"); //Tom goes to the shop

Array syntax

There is also an alternative way to define properties and methods using array syntax:

Var user = (); user["name"] = "Tom"; user["age"] = 26; user["display"] = function())( console.log(user.name); console.log(user.age); ); // calling the method user["display"]();

The name of each property or method is enclosed in quotation marks and square brackets, then it is also assigned a value. For example, user["age"] = 26 .

When accessing these properties and methods, you can either use dot notation (user.name) or use user["name"]

Strings as Properties and Methods

It should also be noted that the names of object properties and methods are always strings. That is, we could rewrite the previous definition of the object like this:

Var user = ( "name": "Tom", "age": 26, "display": function())( console.log(user.name); console.log(user.age); ) ); // calling the method user.display();

On the one hand, there is no difference between the two definitions. On the other hand, there are cases where enclosing the title in a line can help. For example, if the property name consists of two words separated by a space:

Var user = ( name: "Tom", age: 26, "full name": "Tom Johns", "display info": function())( console.log(user.name); console.log(user.age) ; ) ); console.log(user["full name"]); user["display info"]();

Only in this case, to access such properties and methods, we must use array syntax.

Removing properties

Above we looked at how we can dynamically add new properties to an object. However, we can also delete properties and methods using the delete operator. And just like with adding, we can remove properties in two ways. The first way is to use dot notation:

Delete object.property

Or use array syntax:

Delete object["property"]

For example, let's remove the property:

Var user = (); user.name = "Tom"; user.age = 26; user.display = function())( console.log(user.name); console.log(user.age); ); console.log(user.name); // Tom delete user.name; // delete the property // alternative // delete user["name"]; console.log(user.name); // undefined

After deletion, the property will be undefined, so when you try to access it, the program will return the value undefined.

The task :

1. There are three objects (three cars): first_Car, second_Car and third_Car.

2. Each of the objects (cars) has a set of properties and their corresponding values (car characteristics).

3. Consider one of the objects:

var first_Car = (
make: "VAZ" , /* manufacturer */
model: 2106 , /* model */
year: 1980 , /* year of manufacture */
color: "beige" , /* color */
passengers: 5 , /* number of passengers */
convertible: false, /* convertible top */
mileage: 80000 /* mileage */
}

The make and color properties have string values;

The model , year , passengers and mileage properties are numeric values;

The convertible property takes a boolean value.

You need to do the following:

Write a function that checks a car using two parameters (year of manufacture and mileage) and returns the boolean value true or false .

Details:

1. The function has one parameter car , which receives one of 3 objects. For example, the car discussed above is first_Car.

2. The function must work with any similar object.

Function to check object - true or false

/* 1st object */
var first_Car = (
make: "VAZ",
model: 2106,
year: 1980,
color: "beige",
passengers: 5,
convertible: false,
mileage: 80000
}

/* 2nd object */
var second_Car = (
make: "VW",
model: "Passat b3",
year: 1990,
color: "neptune",
passengers: 5,
convertible: false,
mileage: 160000
}

/* 3rd object */
var third_Car = (
make: "Hyundai",
model: "Solaris",
year: 2012,
color: "wet asphalt",
passengers: 5,
convertible: false,
mileage: 15000
}

function good_Car(car) (
if (car. year< 2000 ){
return false;
}
else if (car. mileage > 50000 )(
return false;
}
else(
return true;
}
}

/* Call a function and output the result */
var result = good_Car ( third_Car );

document. write(result);

Comments on the solution:

So we have three objects (three cars), each of which can be analyzed using the good_Car function.
The good_Car function has one parameter car , which can be any of the objects (cars): first_Car , second_Car or third_Car : function good_Car(car) .
The body of the good_Car Function contains a condition according to which:
If the value of the year property of the car object is less than 2000 (in other words: if the car is less than 2,000 year old), then the function returns false;
Otherwise, if the value of the car object's mileage property is greater than 50000 (if the car's mileage is more than 50,000), then the function returns false;
Otherwise the function returns true.
Next, we call the function and specify the third_Car object as a parameter (third car), which passes the test successfully. The result of the function is stored in the result variable:
var result = good_Car(third_Car); .
The result variable is displayed on the screen;
Two other objects (car) will not meet the requirements of the conditions.

Code optimization

Let's continue working with objects in javascript.

So, the function discussed above when checking objects (cars) returns true or false (true or false).

You can slightly improve the quality of perception of the solution to the problem under consideration, that is, instead of true or false, display some text. To do this, we will create a condition for analyzing the result.

/* 1st object */
var first_Car = (
make: "VAZ",
model: 2106,
year: 1980,
color: "beige",
passengers: 5,
convertible: false,
mileage: 80000
}

/* 2nd object */
var second_Car = (
make: "VW",
model: "Passat b3",
year: 1990,
color: "neptune",
passengers: 5,
convertible: false,
mileage: 160000
}

/* 3rd object */
var third_Car = (
make: "Hyundai",
model: "Solaris",
year: 2012,
color: "wet asphalt",
passengers: 5,
convertible: false,
mileage: 15000
}

/* Function for checking an object */
function good_Car(car) (
if (car. year< 2000 ){
return false;
}
else if (car. mileage > 50000 )(
return false;
}
else(
return true;
}
}

var result = good_Car ( third_Car );

if(result) (
document. write ("You have a good car: " + third_Car . year + " year of manufacture, with mileage " + third_Car .mileage + " km." );
}
else(
document. write("We won't talk about your car....");
}

Solution with a condition for the result - Result...

The condition for analyzing the result is as follows.

The if(result) expression is a shorthand form of the expression
if(result == true) .
If the result of the good_Car function is true, then we display the phrase: “You have a good car: 2012, with a mileage of 15,000 km,” where
2012 and 15000 are the values of the year and mileage properties of the third_Car object.
If the condition for checking the result produces a false value false , then we will see: “We won’t talk about your car...”. That is, the object in question (automobile) did not pass the test.

Code optimization - Moving on - Adding a function

But that's not all. Take a close look at the code snippet for calling the function and parsing the result:

/* Call the function and analyze the result */
var result = good_Car( third_Car );

if(result) (
document.write("You have a good car: " + third_Car .year + " year of manufacture, with mileage " + third_Car .mileage + " km.");
}
else(
document.write("We won't talk about your car....");
}

Here is the third_Car object (third car) indicated three times:

The first time the good_Car function is called, it is specified as its parameter: good_Car(third_Car) .
And then it appears twice more when we access it to indicate its properties: third_Car.year and third_Car.mileage .

I didn't like this because when analyzing another object (car) we will have to indicate his name three times as well!!!

To achieve a one-time indication of the analyzed object, you need both the result of the good_Car function and an analysis of this result (that is, all) put into another function.

/* 1st object */
var first_Car = (
make: "VAZ",
model: 2106,
year: 1980,
color: "beige",
passengers: 5,
convertible: false,
mileage: 80000
}

/* 2nd object */
var second_Car = (
make: "VW",
model: "Passat b3",
year: 1990,
color: "neptune",
passengers: 5,
convertible: false,
mileage: 160000
}

/* 3rd object */
var third_Car = (
make: "Hyundai",
model: "Solaris",
year: 2012,
color: "wet asphalt",
passengers: 5,
convertible: false,
mileage: 15000
}

/* Function for checking an object */
function good_Car(car) (
if (car .year< 2000){
return false;
}
else if (car .mileage > 50000)(
return false;
}
else(
return true;
}
}

/* Enter the result of the good_Car function and Analysis of the result into another function */
function itog(car )(
var result = good_Car(car);

If(result) (
document.write("You have a good car: " + car .year + " year of manufacture, with mileage " + car .mileage + " km.");
}
else(
document.write("We won't talk about your car....");
}
}

itog( third_Car );

Solution using another function - Result...

You have a good car: manufactured in 2012, with a mileage of 15,000 km.

Objects are one of the core concepts in JavaScript. When I first started studying them, they seemed quite simple to me: just pairs of keys and values, as described in theory.

Only after some time did I begin to understand that the topic was much more complex than I thought. And then I began to study information from different sources. Some of them gave good show about the subject, but I was not able to see the whole picture right away.

In this post, I tried to cover all aspects of working with objects in JS, without going too deep into specific details, but also without leaving out important details that will help you understand the subject and feel more confident as you study it further.

So let's start with the basics.

ObjectAn object in JavaScript is simply a collection of properties, each of which is a key-value pair. You can access the keys using a dot ( obj.a) or bracket notation ( obj["a"]).

Remember that parentheses should be used if the key is:

is not a valid JavaScript identifier (it has a space, a dash, starts with a number...)
is a variable.

One of the properties that objects in JS receive when created is called Prototype, and this is a very important concept. Prototype Every object in JavaScript has an internal property called Prototype. In most browsers you can refer to it by the notation __proto__.

Prototype is a way to enforce property inheritance in JavaScript. This way you can share functionality without duplicating code in memory. The method works by creating a connection between two objects.

Simply put, Prototype creates a pointer from one object to another.

Prototype chain

Every time JS looks for a property in an object and does not find it directly on the object itself, it checks for the presence of the property in the prototype object. If there is no property in it, then JS will continue to look in the prototype of the associated object. This will continue until JS finds a suitable property or reaches the end of the chain.

Let's look at an example:

Var cons = function () ( this.a = 1; this.b = 2; ) var obj = new cons(); cons.prototype.b = 3; cons.prototype.c = 4;
cons is a constructor (simply a function that can be called using the operator new).

On the fifth line we create a new object - a new copy cons. Immediately after creation obj also gets the prototype property.

And now we add properties ( "b", "c") object prototype cons.
Let's consider obj:

obj.a // 1 - everything is the same here, obj.a is still 1.
obj.c? - y obj no property c! However, as previously mentioned, JS will now look for it in the prototype obj and will return the value 4.

Now let's think about what the meaning is obj.b and what it will be like when we remove obj.b?

Obj.b is equal to 2. We assigned the property b, but we did it for a prototype cons, so when we check obj.b, then we still get 2. However, immediately after removing obj.b JS will no longer be able to find b y o bj, and therefore will continue searching in the prototype and return the value 3.

Creating an object Literal object: let obj = (a: 1);
We created an object with the following prototype chain: obj ---> Object.prototype ---> null
As you can guess, object.prototype is the prototype of the object, and also the end of the prototype chain.

Object.create(): var newObj = Object.create(obj);
U newObj there will be the following chain of prototypes: newObj ---> obj ---> Object.prototype ---> null

Constructor. As in the example above, the constructor is simply a JS function that allows us to use the operator new to create new instances of it.

ES6 classes:

Class rectangle ( constructor(height, width) ( this.height = height; this.width = width; ) getArea() ( return this.height * this.width; ) ) let square = new rectangle(2, 2);
Square- constructor instance rectangle, and so we can call square.getArea() //4, square.width, as well as all functions inherited from object.prototype.

Which way is better? If you plan to create multiple instances, you can use ES6 or the designer. If you plan to create the object once, then it is better to specify a literal, since this is the simplest way.

And now that we have learned about prototype and having become familiar with all the ways to create new objects, we can move on to discuss one of the most confusing aspects associated with objects.

Comparing and Modifying Objects In JavaScript, objects are reference types.

When we create an object let obj = (a: 1);, variable obj gets the object's memory address, but not its value! It is extremely important to understand this difference, as otherwise errors may occur. When we create another object let newObj = obj, we actually create a pointer to a certain memory area obj, and not a completely new object.

This means that by doing newObj.a = 2, we actually change obj so that obj.a becomes equal to 2!

This approach easily leads to bugs, which is why many companies work with immutable objects. Instead of changing an already created object, you will have to again create a new object (a copy of the original) and make changes to it. This is how important libraries like Redux work, and it is one of the core concepts of functional programming in general. You can read more.

Equality

It also follows from the above that two objects can never be equal, even if they have the same properties. This is due to the fact that JS actually compares the memory location of objects, and two objects are never in the same memory location.

// Two distinct objects with the same properties are not equal var fruit = (name: "apple"); var fruitbear = (name: "apple"); fruit === fruitbear; // return false // here fruit and fruitbear are pointing to the same object var fruit = (name: "apple"); var fruitbear = fruit; fruit === fruitbear; // return true
So, you most likely have already wondered how you can compare objects or how to perform various manipulations with objects, given the requirement for their immutability.

Let's consider several possibilities.

Changing an object

Let's say it's clear that we shouldn't actually change objects, so we want to create a copy of the corresponding object and change its properties. Comes to the rescue Object.assign().

Var obj = (a: 1, b: 2); var newObj = Object.assign((), obj,(a:2)) // (a: 2, b: 2 )
If we want to change the property value a object obj, you can use object.assign to create a copy obj and its changes.

In the example you can see that we first create an empty object, then copy the values obj and make our changes, ultimately obtaining a new and ready-to-use object.

Please note that this method will not work for deep copying. When we talk about deep copying, we mean that we need to copy an object with one or more properties.

Const obj = (a: 1, b: ( a: 1 ) ); // b property is an object
Object.assign() copies the properties of an object, so if the value of the property is a pointer to an object, then only the pointer is copied.

A deep copy requires a recursive operation. Here you can write a function or just use a method _.cloneDeep from the Lodash library.

Comparison of objects

There is one cool technique for working with objects - string conversion. In the following example, we convert both objects to strings and compare them:

JSON.stringify(obj1) === JSON.stringify(obj2)
This approach makes sense because we end up comparing strings that are a pointer to a value type. The bad news is that it doesn't always work, mainly because the order of the object's properties is not guaranteed.

Another good solution is to use the method _.isEqual from Lodash, which performs deep object comparison.

And before we wrap up, let's go over some frequently asked questions about objects. This will help you dive deeper into the topic and apply the acquired knowledge in practice.

Try to think about the solution yourself before reading the answer.

How to find out the length of an object? To get the answer, you need to go through all the properties of the object one by one and count them. There are several ways to perform such an iteration:

for in. This method covers all countable properties of an object and its prototype chains. We've seen the prototype (and hopefully learned the material), so it should be clear that the application for in won't always be true for getting properties of an object.
Object.keys. This method returns an array with the keys of all the native (belonging to the specified object) counting properties. This approach is better because we only work on the properties of the object, without accessing the properties prototype. There are, however, situations where you have assigned an attribute enumerable some property is false, and object.keys ends up skipping it, and you get an incorrect result. This rarely happens, but in such cases it will come in handy getOwnPropertyNames.
getOwnPropertyNames returns an array containing all of the object's own keys (both countable and uncountable).

Also worth mentioning:

Object.values iterates over its own counting properties and returns an array with the corresponding values.
Object.entries iterates over its own counting properties and returns an array with the keys and their values.

I think you noticed that most of the methods listed above return an array. This is an opportunity to take full advantage of JavaScript's array techniques.

One such method is array.length. As a result, we can simply write

Let objLength = Object.getOwnPropertyNames(obj).length;

How to check if an object is empty?

JSON.stringify(myObj) === “()”?. Here we again use the string conversion tool to easily check whether an object is empty (by comparing strings, not objects).

!Object.keys(myobj).length // true?.? As I mentioned, converting an object's keys to an array can be very useful. Here we use the convenient property length, inherited from Array.prototype, using it to check the length of the keys in the array. In JS 0 turns to false, so adding ! we turn it to true. Any other numbers will be converted to false.

In conclusion I hope you now feel more confident in creating and working with objects. Let's summarize:

Remember that objects are of a reference type, which means that it is recommended to work with them without changing the original objects.
Make friends with the property prototype and a chain of prototypes.
Get to know the tools that help you work with objects. Remember that you can turn objects into strings, get an array of their keys, or simply iterate over their properties using the set of methods we've been introduced to.

Good luck learning JavaScript objects.