JavaScript Datatypes
JavaScript has 8 Datatypes
A JavaScript variable can hold 8 types of data:
| Type | Description |
|---|---|
| String | A text of characters enclosed in quotes |
| Number | A number representing a mathematical value |
| Bigint | A number representing a large integer |
| Boolean | A data type representing true or false |
| Object | A collection of key-value pairs of data |
| Undefined | A primitive variable with no assigned value |
| Null | A primitive value representing object absence |
| Symbol | A unique and primitive identifier |
Examples
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 JavaScripttypeof operator to find the type of a JavaScript variable.
Thetypeof operator returns the type of a variable or an expression:
Example
typeof "John" // Returns "string"
typeof "John Doe" // Returns "string"
Example
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
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
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 aboutJavaScript 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:
Exponential Notation
Extra large or extra small numbers can be written with scientific (exponential) notation:
JavaScript Booleans
JavaScript booleans can only have one of two values:true orfalse
The boolean value of an expression is the basis for JavaScript comparisons.
Given thatx = 5, the table below explains comparison:
| Description | Expression | Returns |
|---|---|---|
| Equal to | (x == 8) | false |
| Not equal to | (x != 8) | true |
| Greater than | (x > 8) | false |
| Less than | (x < 8) | true |
Note
All JavaScript comparison operators (like ==, !=, <, >)returntrue orfalse 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 datatypeundefined.
A variable without a value also has the valueundefined.
Empty Values
An empty value has nothing to do withundefined.
An empty string has both a legal value and a type.
Note
You will learn a lot more aboutData Types later in this tutorial.
