Source: JavaScript Objects (w3schools.com)
In JavaScript, objects are king. If you understand objects, you understand JavaScript.
In JavaScript, almost "everything" is an object.
- Booleans can be objects (if defined with the
new
keyword) - Numbers can be objects (if defined with the
new
keyword) - Strings can be objects (if defined with the
new
keyword) - Dates are always objects
- Maths are always objects
- Regular expressions are always objects
- Arrays are always objects
- Functions are always objects
- Objects are always objects
All JavaScript values, except primitives, are objects.
JavaScript Primitives
A primitive value is a value that has no properties or methods.
3.14 is a primitive value
A primitive data type is data that has a primitive value.
JavaScript defines 7 types of primitive data types:
Examples
string
number
boolean
null
undefined
symbol
bigint
A JavaScript object is a collection of named values
It is a common practice to declare objects with the const
keyword.
Example
const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
Object Properties
The named values, in JavaScript objects, are called properties.
Property | Value |
---|---|
firstName | John |
lastName | Doe |
age | 50 |
eyeColor | blue |
Objects written as name value pairs are similar to:
- Associative arrays in PHP
- Dictionaries in Python
- Hash tables in C
- Hash maps in Java
- Hashes in Ruby and Perl
Object Methods
Methods are actions that can be performed on objects.
Object properties can be both primitive values, other objects, and functions.
An object method is an object property containing a function definition.
Property | Value |
---|---|
firstName | John |
lastName | Doe |
age | 50 |
eyeColor | blue |
fullName | function() {return this.firstName + " " + this.lastName;} |
JavaScript objects are containers for named values, called properties and methods.
Creating a JavaScript Object
With JavaScript, you can define and create your own objects.
There are different ways to create new objects:
- Create a single object, using an object literal.
- Create a single object, with the keyword
new
. - Define an object constructor, and then create objects of the constructed type.
- Create an object using
Object.create()
.
Using an Object Literal
This is the easiest way to create a JavaScript Object.
Using an object literal, you both define and create an object in one statement.
An object literal is a list of name:value pairs (like age:50) inside curly braces {}.
The following example creates a new JavaScript object with four properties:
Example
const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
Spaces and line breaks are not important. An object definition can span multiple lines:
Example
const person = {
firstName: "John",
lastName: "Doe",
age: 50,
eyeColor: "blue"
};
This example creates an empty JavaScript object, and then adds 4 properties:
Example
const person = {};
person.firstName = "John";
person.lastName = "Doe";
person.age = 50;
person.eyeColor = "blue";
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