Objects 

Let user = {     // an object
  name: "John",  // by key "name" store value "John"
  age: 30        // by key "age" store value 30
};
Let fruit = prompt("Which fruit to buy?", "apple");

let bag = {
*!*
  [fruit]: 5, // the name of the property is taken from the variable fruit
*/!*
};

alert( bag.apple ); // 5 if fruit="apple"
  • Are used to store keyed collections of various data and more complex entities.
  • We can immediately put some properties into {...} as "key: value" pairs.
  • We can use square brackets in an object literal. That's called computed properties.
  • A notable feature is that it's possible to access any property. There will be no error if the property doesn't exist! Accessing a non-existing property just returns undefined.
  • One of the fundamental differences of objects vs primitives is that they are stored and copied "by reference".
  • Is capable of storing multiple values as properties.
  • For more complex data structures.

Syntax

Let user = new Object(); // "object constructor" syntax
let user = {};  // "object literal" syntax
Can be created with figure brackets {…} with an optional list of properties. A property is a "key: value" pair, where key is a string (also called a "property name"), and value can be anything.

Related concepts

→
Objects
→

Objects — Structure map

Clickable & Draggable!

Objects — Related pages:

Object-oriented programming

XMLHttpRequest and AJAX

Async/await

Promise API

Mixins

Classes