Menu
×
   ❮     
HTML CSS JAVASCRIPT SQL PYTHON JAVA PHP HOW TO W3.CSS C C++ C# BOOTSTRAP REACT MYSQL JQUERY EXCEL XML DJANGO NUMPY PANDAS NODEJS R TYPESCRIPT ANGULAR GIT POSTGRESQL MONGODB ASP AI GO KOTLIN SASS VUE DSA GEN AI SCIPY AWS CYBERSECURITY DATA SCIENCE
     ❯   

JS Tutorial

JS HOME JS Introduction JS Where To JS Output JS Statements JS Syntax JS Comments JS Variables JS Let JS Const JS Operators JS Arithmetic JS Assignment JS Data Types JS Functions JS Objects JS Object Properties JS Object Methods JS Object Display JS Object Constructors JS Events JS Strings JS String Methods JS String Search JS String Templates JS Numbers JS BigInt JS Number Methods JS Number Properties JS Arrays JS Array Methods JS Array Search JS Array Sort JS Array Iteration JS Array Const JS Dates JS Date Formats JS Date Get Methods JS Date Set Methods JS Math JS Random JS Booleans JS Comparisons JS If Else JS Switch JS Loop For JS Loop For In JS Loop For Of JS Loop While JS Break JS Iterables JS Sets JS Set Methods JS Maps JS Map Methods JS Typeof JS Type Conversion JS Destructuring JS Bitwise JS RegExp JS Precedence JS Errors JS Scope JS Hoisting JS Strict Mode JS this Keyword JS Arrow Function JS Classes JS Modules JS JSON JS Debugging JS Style Guide JS Best Practices JS Mistakes JS Performance JS Reserved Words

JS Versions

JS Versions JS 2009 (ES5) JS 2015 (ES6) JS 2016 JS 2017 JS 2018 JS 2019 JS 2020 JS 2021 JS 2022 JS 2023 JS 2024 JS IE / Edge JS History

JS Objects

Object Definitions Object Prototypes Object Methods Object Properties Object Get / Set Object Protection

JS Functions

Function Definitions Function Parameters Function Invocation Function Call Function Apply Function Bind Function Closures

JS Classes

Class Intro Class Inheritance Class Static

JS Async

JS Callbacks JS Asynchronous JS Promises JS Async/Await

JS HTML DOM

DOM Intro DOM Methods DOM Document DOM Elements DOM HTML DOM Forms DOM CSS DOM Animations DOM Events DOM Event Listener DOM Navigation DOM Nodes DOM Collections DOM Node Lists

JS Browser BOM

JS Window JS Screen JS Location JS History JS Navigator JS Popup Alert JS Timing JS Cookies

JS Web APIs

Web API Intro Web Forms API Web History API Web Storage API Web Worker API Web Fetch API Web Geolocation API

JS AJAX

AJAX Intro AJAX XMLHttp AJAX Request AJAX Response AJAX XML File AJAX PHP AJAX ASP AJAX Database AJAX Applications AJAX Examples

JS JSON

JSON Intro JSON Syntax JSON vs XML JSON Data Types JSON Parse JSON Stringify JSON Objects JSON Arrays JSON Server JSON PHP JSON HTML JSON JSONP

JS vs jQuery

jQuery Selectors jQuery HTML jQuery CSS jQuery DOM

JS Graphics

JS Graphics JS Canvas JS Plotly JS Chart.js JS Google Chart JS D3.js

JS Examples

JS Examples JS HTML DOM JS HTML Input JS HTML Objects JS HTML Events JS Browser JS Editor JS Exercises JS Quiz JS Website JS Syllabus JS Study Plan JS Interview Prep JS Bootcamp JS Certificate

JS References

JavaScript Objects HTML DOM Objects


JavaScript Statements


Example

let x, y, z;    // Statement 1
x = 5;          // Statement 2
y = 6;          // Statement 3
z = x + y;      // Statement 4
Try it Yourself »

JavaScript Programs

A computer program is a list of "instructions" to be "executed" by a computer.

In a programming language, these programming instructions are called statements.

A JavaScript program is a list of programming statements.

In HTML, JavaScript programs are executed by the web browser.


JavaScript Statements

JavaScript statements are composed of:

Values, Operators, Expressions, Keywords, and Comments.

This statement tells the browser to write "Hello Dolly." inside an HTML element with id="demo":

Example

document.getElementById("demo").innerHTML = "Hello Dolly.";
Try it Yourself »

Most JavaScript programs contain many JavaScript statements.

The statements are executed, one by one, in the same order as they are written.

JavaScript programs (and JavaScript statements) are often called JavaScript code.


Semicolons ;

Semicolons separate JavaScript statements.

Add a semicolon at the end of each executable statement:

Examples

let a, b, c;  // Declare 3 variables
a = 5;        // Assign the value 5 to a
b = 6;        // Assign the value 6 to b
c = a + b;    // Assign the sum of a and b to c
Try it Yourself »

When separated by semicolons, multiple statements on one line are allowed:

a = 5; b = 6; c = a + b;
Try it Yourself »

On the web, you might see examples without semicolons.
Ending statements with semicolon is not required, but highly recommended.



JavaScript White Space

JavaScript ignores multiple spaces. You can add white space to your script to make it more readable.

The following lines are equivalent:

let person = "Hege";
let person="Hege";

A good practice is to put spaces around operators ( = + - * / ):

let x = y + z;

JavaScript Line Length and Line Breaks

For best readability, programmers often like to avoid code lines longer than 80 characters.

If a JavaScript statement does not fit on one line, the best place to break it is after an operator:

Example

document.getElementById("demo").innerHTML =
"Hello Dolly!";
Try it Yourself »

JavaScript Code Blocks

JavaScript statements can be grouped together in code blocks, inside curly brackets {...}.

The purpose of code blocks is to define statements to be executed together.

One place you will find statements grouped together in blocks, is in JavaScript functions:

Example

function myFunction() {
  document.getElementById("demo1").innerHTML = "Hello Dolly!";
  document.getElementById("demo2").innerHTML = "How are you?";
}
Try it Yourself »

In this tutorial we use 2 spaces of indentation for code blocks.
You will learn more about functions later in this tutorial.


JavaScript Keywords

JavaScript statements often start with a keyword to identify the JavaScript action to be performed.

Our Reserved Words Reference lists all JavaScript keywords.

Here is a list of some of the keywords you will learn about in this tutorial:

Keyword Description
var Declares a variable
let Declares a block variable
const Declares a block constant
if Marks a block of statements to be executed on a condition
switch Marks a block of statements to be executed in different cases
for Marks a block of statements to be executed in a loop
function Declares a function
return Exits a function
try Implements error handling to a block of statements

JavaScript keywords are reserved words. Reserved words cannot be used as names for variables.


×

Contact Sales

If you want to use W3Schools services as an educational institution, team or enterprise, send us an e-mail:
sales@w3schools.com

Report Error

If you want to report an error, or if you want to make a suggestion, send us an e-mail:
help@w3schools.com

W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. While using W3Schools, you agree to have read and accepted our terms of use, cookie and privacy policy.

Copyright 1999-2024 by Refsnes Data. All Rights Reserved. W3Schools is Powered by W3.CSS.