Create object by name javascript

Object.create()

The Object.create() static method creates a new object, using an existing object as the prototype of the newly created object.

Try it

Syntax

.create(proto) Object.create(proto, propertiesObject) 

Parameters

The object which should be the prototype of the newly-created object.

If specified and not undefined , an object whose enumerable own properties specify property descriptors to be added to the newly-created object, with the corresponding property names. These properties correspond to the second argument of Object.defineProperties() .

Return value

A new object with the specified prototype object and properties.

Exceptions

Thrown if proto is neither null nor an Object .

Examples

Classical inheritance with Object.create()

Below is an example of how to use Object.create() to achieve classical inheritance. This is for a single inheritance, which is all that JavaScript supports.

// Shape - superclass function Shape()  this.x = 0; this.y = 0; > // superclass method Shape.prototype.move = function (x, y)  this.x += x; this.y += y; console.info("Shape moved."); >; // Rectangle - subclass function Rectangle()  Shape.call(this); // call super constructor. > // subclass extends superclass Rectangle.prototype = Object.create(Shape.prototype,  // If you don't set Rectangle.prototype.constructor to Rectangle, // it will take the prototype.constructor of Shape (parent). // To avoid that, we set the prototype.constructor to Rectangle (child). constructor:  value: Rectangle, enumerable: false, writable: true, configurable: true, >, >); const rect = new Rectangle(); console.log("Is rect an instance of Rectangle?", rect instanceof Rectangle); // true console.log("Is rect an instance of Shape?", rect instanceof Shape); // true rect.move(1, 1); // Logs 'Shape moved.' 

Note that there are caveats to watch out for using create() , such as re-adding the constructor property to ensure proper semantics. Although Object.create() is believed to have better performance than mutating the prototype with Object.setPrototypeOf() , the difference is in fact negligible if no instances have been created and property accesses haven’t been optimized yet. In modern code, the class syntax should be preferred in any case.

Using propertiesObject argument with Object.create()

Object.create() allows fine-tuned control over the object creation process. The object initializer syntax is, in fact, a syntax sugar of Object.create() . With Object.create() , we can create objects with a designated prototype and also some properties. Note that the second parameter maps keys to property descriptors — this means you can control each property’s enumerability, configurability, etc. as well, which you can’t do in object initializers.

= >; // Is equivalent to: o = Object.create(Object.prototype); o = Object.create(Object.prototype,  // foo is a regular data property foo:  writable: true, configurable: true, value: "hello", >, // bar is an accessor property bar:  configurable: false, get()  return 10; >, set(value)  console.log("Setting `o.bar` to", value); >, >, >); // Create a new object whose prototype is a new, empty // object and add a single property 'p', with value 42. o = Object.create(>,  p:  value: 42 > >); 

With Object.create() , we can create an object with null as prototype. The equivalent syntax in object initializers would be the __proto__ key.

= Object.create(null); // Is equivalent to: o =  __proto__: null >; 

By default properties are not writable, enumerable or configurable.

.p = 24; // throws in strict mode o.p; // 42 o.q = 12; for (const prop in o)  console.log(prop); > // 'q' delete o.p; // false; throws in strict mode 

To specify a property with the same attributes as in an initializer, explicitly specify writable , enumerable and configurable .

= Object.create( >,  p:  value: 42, writable: true, enumerable: true, configurable: true, >, >, ); // This is not equivalent to: // o2 = Object.create(< p: 42 >) // which will create an object with prototype 

You can use Object.create() to mimic the behavior of the new operator.

function Constructor() > o = new Constructor(); // Is equivalent to: o = Object.create(Constructor.prototype); 

Of course, if there is actual initialization code in the Constructor function, the Object.create() method cannot reflect it.

Specifications

Browser compatibility

BCD tables only load in the browser

See also

Found a content problem with this page?

This page was last modified on Feb 21, 2023 by MDN contributors.

Your blueprint for a better internet.

Источник

How to create objects in JavaScript

We all deal with objects in one way or another while writing code in a programming language. In JavaScript, objects provide a way for us to store, manipulate, and send data over the network.

There are many ways in which objects in JavaScript differ from objects in other mainstream programming languages, like Java. I will try to cover that in a another topic. Here, let us only focus on the various ways in which JavaScript allows us to create objects.

In JavaScript, think of objects as a collection of ‘key:value’ pairs. This brings to us the first and most popular way we create objects in JavaScript.

1. Creating objects using object literal syntax

This is really simple. All you have to do is throw your key value pairs separated by ‘:’ inside a set of curly braces(< >) and your object is ready to be served (or consumed), like below:

This is the simplest and most popular way to create objects in JavaScript.

2. Creating objects using the ‘new’ keyword

This method of object creation resembles the way objects are created in class-based languages, like Java. By the way, starting with ES6, classes are native to JavaScript as well and we will look at creating objects by defining classes towards the end of this article. So, to create an object using the ‘new’ keyword, you need to have a constructor function.

Here are 2 ways you can use the ‘new’ keyword pattern —

a) Using the ‘new’ keyword with’ in-built Object constructor function

To create an object, use the new keyword with Object() constructor, like this:

Now, to add properties to this object, we have to do something like this:

person.firstName = 'testFirstName'; person.lastName = 'testLastName';

You might have figured that this method is a bit longer to type. Also, this practice is not recommended as there is a scope resolution that happens behind the scenes to find if the constructor function is built-in or user-defined.

b) Using ‘new’ with user defined constructor function

The other problem with the approach of using the ‘Object’ constructor function result from the fact that every time we create an object, we have to manually add the properties to the created object.

What if we had to create hundreds of person objects? You can imagine the pain now. So, to get rid of manually adding properties to the objects, we create custom (or user-defined) functions. We first create a constructor function and then use the ‘new’ keyword to get objects:

function Person(fname, lname)

Now, anytime you want a ‘Person’ object, just do this:

const personOne = new Person('testFirstNameOne', 'testLastNameOne'); const personTwo = new Person('testFirstNameTwo', 'testLastNameTwo');

3. Using Object.create() to create new objects

This pattern comes in very handy when we are asked to create objects from other existing objects and not directly using the ‘new’ keyword syntax. Let’s see how to use this pattern. As stated on MDN:

The Object.create() method creates a new object, using an existing object as the prototype of the newly created object.

To understand the Object.create method, just remember that it takes two parameters. The first parameter is a mandatory object that serves as the prototype of the new object to be created. The second parameter is an optional object which contains the properties to be added to the new object.

We will not deep dive into prototypes and inheritance chains now to keep our focus on the topic. But as a quick point, you can think of prototypes as objects from which other objects can borrow properties/methods they need.

Imagine you have an organization represented by orgObject

And you want to create employees for this organization. Clearly, you want all the employee objects.

const employee = Object.create(orgObject, < name: < value: 'EmployeeOne' >>); console.log(employee); // < company: "ABC Corp" >console.log(employee.name); // "EmployeeOne"

4. Using Object.assign() to create new objects

What if we want to create an object that needs to have properties from more than one object? Object.assign() comes to our help.

The Object.assign() method is used to copy the values of all enumerable own properties from one or more source objects to a target object. It will return the target object.

Object.assign method can take any number of objects as parameters. The first parameter is the object that it will create and return. The rest of the objects passed to it will be used to copy the properties into the new object. Let’s understand it by extending the previous example we saw.

Assume you have two objects as below:

const orgObject = < company: 'ABC Corp' >const carObject =

Now, you want an employee object of ‘ABC Corp’ who drives a ‘Ford’ car. You can do that with the help of Object.assign as below:

const employee = Object.assign(<>, orgObject, carObject);

Now, you get an employee object that has company and carName as its property.

5. Using ES6 classes to create objects

You will notice that this method is similar to using ‘new’ with user defined constructor function. The constructor functions are now replaced by classes as they are supported through ES6 specifications. Let’s see the code now.

class Person < constructor(fname, lname) < this.firstName = fname; this.lastName = lname; >> const person = new Person('testFirstName', 'testLastName'); console.log(person.firstName); // testFirstName console.log(person.lastName); // testLastName 

These are all the ways I know to create objects in JavaScript. I hope you enjoyed this post and now understand how to create objects.

Thanks for your time for reading this article. If you liked this post and it was helpful to you, please click the clap ? button to show your support. Keep learning more!

Источник

JavaScript. Создание объектов

Это, наверное, самый легкий способ создания объекта. Вы просто создаете имя объекта и приравниваете его к новому объекту Javascript.

//Создаем наш объект var MyObject = new Object(); //Переменные MyObject.id = 5; //Число MyObject.name = «Sample»; //Строка //Функции MyObject.getName = function()

Минус данного способа заключается в том, что вы можете работать только с одним вновь созданным объектом.

//Используем наш объект alert(MyObject.getName());

Литеральная нотация

Литеральная нотация является несколько непривычным способом определения новых объектов, но достаточно легким для понимания. Литеральная нотация работает с версии Javascript 1.3.

//Создаем наш объект с использованием литеральной нотации MyObject = < id : 1, name : "Sample", boolval : true, getName : function() < return this.name; >>

Как видите, это довольно просто.

Конструкторы объектов

Конструкторы объектов — это мощное средство для создания объектов, которые можно использовать неоднократно. Конструктор объекта — это, по сути, обычная функция Javascript, которой так же можно передавать различные параметры.

Только что мы написали конструтор. С помощью него мы и будем создавать наш объект.

var MyFirstObjectInstance = new MyObject(5,"Sample"); var MySecondObjectInstace = new MyObject(12,"Othe Sample");

Таким образом мы создали различные экземпляры объекта. Теперь мы можем работать отдельно с каждым экземпляром объекта MyObject, не боясь того, что, изменяя свойства одного экземпляра, мы затронем свойства другого экземпляра.

Как и в ООП, у MyObject могут быть методы и различные свойства. Свойствам можно присвоить значения по умолчанию, либо значения, переданные пользователем в конструкторе объекта.

Аналогичным образом мы можем создавать и функции.

function MyObject(id,name) < this._id = id; this._name = name; this.defaultvalue = "MyDefaultValue"; //Получение текущего значения this.getDefaultValue = function() < return this.defaultvalue; >//Установка нового значения this.setDefaultValue = function(newvalue) < this.defaultvalue = newvalue; >//Произвольная функция this.sum = function(a, b) < return (a+b); >>

Ассоциативные массивы

Подобный метод будет полезен упорядочивания большого числа однотипных объектов.

var MyObject = new Number(); MyObject["id"] = 5; MyObject["name"] = "SampleName";

Для обхода таких объектов можно использовать такой цикл:

for (MyElement in MyObject) < //Код обхода //В MyElement - идентификатор записи //В MyObject[MyElement] - содержание записи >

По материалу подготовлена небольшая схема.

Вы можете её посмотреть в форматах: PNG SVG

Огромное спасибо gro за помощь.

Источник