JavaScript Datatypes
JavaScript has 8 DatatypesA 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
// Strings
let color = "Yellow";
let lastName = "Johnson";
// Numbers
let length = 16;
let weight = 7.5;
// Bigint
let x = 1234567890123456789012345n;
let y = BigInt(1234567890123456789012345)
// Booleans
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"
Try it Yourself »
Example
typeof 0 // Returns
"number"
typeof 314 // Returns
"number"
typeof 3.14 // Returns
"number"
typeof (3) // Returns
"number"
typeof (3 + 4) // Returns
"number"
Try it Yourself »
Note
You will learn a lot more about Data Types later in this tutorial.
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';
Try
it Yourself »
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"';
Try
it Yourself »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:
Exponential Notation
Extra large or extra small numbers can be written with scientific (exponential) notation:
Note
Most programming languages have many number types:
Whole numbers (integers):
byte (8-bit), short (16-bit), int (32-bit), long (64-bit)
Real numbers (floating-point):
float (32-bit), double (64-bit).
Javascript numbers are always double (64-bit floating point).
You will learn a lot more about JavaScript Numbers later in this tutorial.
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.
Empty Values
An empty value has nothing to do with undefined.
An empty string has both a legal value and a type.
Re-Declaring JavaScript Variables
If you re-declare a JavaScript variable declared with var, it will not lose its value.
The variable carName will still have the value "Volvo" after the execution of these statements:
You cannot re-declare a variable declared with let or const.
Example
This will not work:
let carName = "Volvo";
let carName;
Example
This will not work:
const carName = "Volvo";
const carName;
