JavaScript Built-In Objects

A JavaScript variable can be either a Primitive type or an Object type.

The Object data type can hold many different object types.

Examples

// Object
const person = {firstName:"John", lastName:"Doe"};

// Array Object
const cars = ["Saab", "Volvo", "BMW"];

// Date Object
const date = new Date("2022-03-25");

JavaScript Objects

JavaScript Objects represent complex data structures and functionalities beyond the primitive data types (string, number, boolean, null, undefined, symbol, bigint).

JavaScript objects are written with curly braces { }.

JavaScript objects contains a collection of different properties.

Object properties are written as name:value pairs, separated by commas.

Example

Create a person object with 4 properties: firstName, lastName, age and eyeColor:

const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};

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Learn More:

JavaScript Object Tutorial

Built-In Object Types

A JavaScript object can represent a JavScript object or a User defined object.

Built-in JavavaScript object types can be:

Object	Description
Array	Array of values accessed by a numerical index
Map	Array of key-value pairs where the keys can be of any data type
Set	Array of values where each value can only appear once
WeakMap	A type of Map with weak references to the stored objects.
WeakSet	A type of Set with weak references to the stored objects.
Math	An object that provides math constants and functions like PI and random()
Date	Object for working with dates and times
RegExp	Object for working with regular expressions
Error	Object represents error conditions during program execution
JSON	Object with methods for parsing values between JSON and objects
Promise	Object representing the completion or failure of an asynchronous operation
Int8Array	Array for storing fixed-size 8-bits integer values
Int16Array	Array for storing fixed-size 16-bits integer values
Int32Array	Array for storing fixed-size 32-bits integer values
Float16Array	Array for storing fixed-size 16-bits floating-point values
Float32Array	Array for storing fixed-size 32-bits floating-point values
Float64Array	Array for storing fixed-size 64-bits floating-point values
BigInt64Array	Array for storing fixed-size 64-bits big integer values

The typeof Operator

You can use the JavaScript typeof operator to find the type of a JavaScript variable.

The typeof operator returns the type of a variable or an expression:

Example

typeof ""             // Returns "string"
typeof "John"         // Returns "string"
typeof "John Doe"     // Returns "string"

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Example

typeof 0              // Returns "number"
typeof 314            // Returns "number"
typeof 3.14           // Returns "number"
typeof (3)            // Returns "number"
typeof (3 + 4)        // Returns "number"

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