JS Types

JavaScript has 8 Datatypes

A JavaScript variable can hold 8 types of data:

Examples

// String

let color = "Yellow";

let lastName = "Johnson";

// Number

let length = 16;

let weight = 7.5;

// BigInt

let x = 1234567890123456789012345n;

let y = BigInt(1234567890123456789012345)

// Boolean

let x = true;

let y = false;

// Object

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

// Array object

const cars = ["Saab", "Volvo", "BMW"];

// Date object

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

// Undefined

let x;

let y;

// Null

let x = null;

let y = null;

// Symbol

const x = Symbol();

const y = Symbol();

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"

Example

typeof 0              // Returns
 "number"

  typeof 314            // Returns
 "number"

  typeof 3.14           // Returns
 "number"

  typeof (3)            // Returns
 "number"
typeof (3 + 4)        // Returns
 "number"

JavaScript Strings

A string (a text string) is a series of characters like "John Doe".

Strings are written with quotes. You can use single or double quotes:

Example

// Using double quotes:

let carName1 = "Volvo XC60";

// Using single quotes:

let carName2 = 'Volvo XC60';

You can use quotes inside a string, as long as they don't match the quotes surrounding the string:

Example

// Single quote inside double quotes:

let answer1 = "It's alright";

// Single quotes inside double quotes:

let answer2 = "He is called 'Johnny'";

// Double quotes inside single quotes:

let answer3 = 'He is called "Johnny"';

Note: You will learn a lot more about JavaScript Strings later in this tutorial.

JavaScript Numbers

All JavaScript numbers are stored as decimal numbers (floating point).

Numbers can be written with, or without decimals:

Example

// With decimals:

let x1 = 34.00;

// Without decimals:

let x2 = 34;

Exponential Notation

Extra large or extra small numbers can be written with scientific (exponential) notation:

Example

let y = 123e5;    // 12300000

let z = 123e-5;   // 0.00123

JavaScript Booleans

JavaScript booleans can only have one of two values: true or false

The boolean value of an expression is the basis for JavaScript comparisons.

Given that x = 5, the table below explains comparison:

Example

let x = 5;

(x == 8); // equals false

(x != 8); // equals true

Note: All JavaScript comparison operators (like ==, !=, <, >) return true or false from the comparison.

Datatype undefined

In computer programs, variables are often declared without a value. The value can be something that has to be calculated, or something that will be provided later, like user input.

A variable without a value has the datatype undefined.

A variable without a value also has the value undefined.

Example

let carName;

Empty Values

An empty value has nothing to do with undefined.

An empty string has both a legal value and a type.

Example

let car = "";    //
    The value is
    "", the typeof is "string"

Note: You will learn a lot more about Data Types later in this tutorial.