JS Tutorials
JS Introduction
JS Syntax
JS Comments
JS Variables
JS Operators
JS Data Types
JS Functions
JS Objects
JS Numbers
JS Arrays
JS Array Methods
JS Booleans
JS Events
JS Strings
JS Dates
JS Maths
JS Objects
Object Definition
Object Properties
Object Methods
Object Display
Object Prototypes
Object Iterables
Object Sets
Object Maps
Object References
JS Functions
Function Definition
Function Parameters
Function Invocation
Function Call
Function Apply
Function ClosuresJS Classes
Class Intro
Class Inhertitance
Class Static
JS Async
JS Callbacks
JS Aysnchronous
JS Promises
JS ASync/Await
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JS Definition
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
newkeyword) - Numbers can be objects (if defined with the
newkeyword) - Strings can be objects (if defined with the
newkeyword) - 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.
A primitive data type is data that has a primitive value.
JavaScript defines 5 types of primitive data types:
stringnumberbooleannullundefined
Primitive values are immutable (they are hardcoded and therefore cannot be changed).
if x = 3.14, you can change the value of x. But you cannot change the value of 3.14.
| Value | Type | Comment |
|---|---|---|
| "Hello" | string | "Hello" is always "Hello" |
| 3.14 | number | 3.14 is always 3.14 |
| true | boolean | true is always true |
| false | boolean | false is always false |
| null | null (object) | null is always null |
| undefined | undefined | undefined is always undefined |
Objects are Variables
JavaScript variables can contain single values:
Example
let person = "John Doe";
JavaScript variables can also contain many values.
Objects are variables too. But objects can contain many values.
Object values are written as name : value pairs (name and value separated by a colon).
Example
let person = {firstName:"John", lastName:"Doe", age:50,
eyeColor:"blue"};
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"};