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JS Basic
JS HOME
JS Introduction JS How To JS Where To JS Statements JS Comments JS Variables JS Operators JS Comparisons JS If...Else JS Switch JS Popup Boxes JS Functions JS For Loop JS While Loop JS Break Loops JS For...In JS Events JS Try...Catch JS Throw JS Special Text JS Guidelines
JS Objects
JS Objects Intro JS String JS Date JS Array JS Boolean JS Math JS RegExp
JS Advanced
JS Browser JS Cookies JS Validation JS Animation JS Image Maps JS Timing JS Create Object JS Summary
JS Examples
JS Examples JS Objects Examples JS Browser Examples JS HTML DOM Examples JS Quiz JS Exam
JS References
JavaScript Objects HTML DOM Objects
JavaScript Tutorial
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JavaScript is THE scripting language of the Web.
JavaScript is used in millions of Web pages to add
functionality, validate forms, detect browsers, and much more.
Start learning JavaScript now!
Examples in Each Chapter
This JavaScript tutorial contains more than 200 examples!
With our online editor, you can edit the JavaScript code, and click on a button to view the result.
Example
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Click on the "Try it Yourself" button to see how it works.
JavaScript Examples
Learn by 200 examples!
With our editor, you can edit the source code, and click on a test button to view the result.
- JavaScript Examples
- JavaScript Objects Examples
- JavaScript Browser Objects Examples
- JavaScript HTML DOM Examples
JavaScript Quiz Test
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JavaScript References
At W3Schools you will find a complete reference of all JavaScript objects, Browser objects, and the HTML DOM objects. Contains lot of examples!
- JavaScript Built-in objects
- Browser objects
- HTML DOM objects
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JS Basic
JS HOME
JS Introduction JS How To JS Where To JS Statements JS Comments JS Variables JS Operators JS Comparisons JS If...Else JS Switch JS Popup Boxes JS Functions JS For Loop JS While Loop JS Break Loops JS For...In JS Events JS Try...Catch JS Throw JS Special Text JS Guidelines
JS Objects
JS Objects Intro JS String JS Date JS Array JS Boolean JS Math JS RegExp
JS Advanced
JS Browser JS Cookies JS Validation JS Animation JS Image Maps JS Timing JS Create Object JS Summary
JS Examples
JS Examples JS Objects Examples JS Browser Examples JS HTML DOM Examples JS Quiz JS Exam
JS References
JavaScript Objects HTML DOM Objects
JavaScript Introduction
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JavaScript is the most popular scripting language on the internet, and works in all
major browsers, such as Internet Explorer, Firefox, Chrome, Opera, and Safari.
What You Should Already Know
Before you continue you should have a basic understanding of the following:
If you want to study these subjects first, find the tutorials on our Home page.
What is JavaScript?
- JavaScript was designed to add interactivity to HTML pages
- JavaScript is a scripting language
- A scripting language is a lightweight programming language
- JavaScript is usually embedded directly into HTML pages JavaScript is an interpreted language (means that scripts execute without preliminary compilation)
- Everyone can use JavaScript without purchasing a license
Are Java and JavaScript the same?
NO!
Java and JavaScript are two completely different languages in both concept and design!
Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in the same category as C and C++.
What can a JavaScript do?
JavaScript gives HTML designers a programming tool - HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages
JavaScript can put dynamic text into an HTML page - A JavaScript statement like this: document.write("" + name + "") can write a variable text into an HTML page
JavaScript can react to events - A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element
JavaScript can read and write HTML elements - A JavaScript can read and change the content of an HTML element
JavaScript can be used to validate data - A JavaScript can be used to validate form data before it is submitted to a server. This saves the server from extra processing
JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser
JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve information on the visitor's computer
The Real Name is ECMAScript
JavaScript's official name is ECMAScript.
ECMAScript is developed and maintained by the ECMA organization.
ECMA-262 is the official JavaScript standard.
The language was invented by Brendan Eich at Netscape (with Navigator 2.0), and has appeared in all Netscape and Microsoft browsers since 1996.
The development of ECMA-262 started in 1996, and the first edition of was adopted by the ECMA General Assembly in June 1997.
The standard was approved as an international ISO (ISO/IEC 16262) standard in 1998.
The development of the standard is still in progress.
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The two forward slashes at the end of comment line (//) is the JavaScript comment symbol. This prevents JavaScript from executing the --> tag.
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JS Basic
JS HOME
JS Introduction JS How To JS Where To JS Statements JS Comments JS Variables JS Operators JS Comparisons JS If...Else JS Switch JS Popup Boxes JS Functions JS For Loop JS While Loop JS Break Loops JS For...In JS Events JS Try...Catch JS Throw JS Special Text JS Guidelines
JS Objects
JS Objects Intro JS String JS Date JS Array JS Boolean JS Math JS RegExp
JS Advanced
JS Browser JS Cookies JS Validation JS Animation JS Image Maps JS Timing JS Create Object JS Summary
JS Examples
JS Examples JS Objects Examples JS Browser Examples JS HTML DOM Examples JS Quiz JS Exam
JS References
JavaScript Objects HTML DOM Objects
JavaScript Where To
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JavaScripts can be put in the body and in the head sections of an HTML page.
Where to Put the JavaScript
JavaScripts in a page will be executed immediately while the page loads into the browser. This is not always what we want. Sometimes we want to execute a script when a page loads, or at a later event, such as when a user clicks a button. When this is the case we put the script inside a function, you will learn about functions in a later chapter.
Scripts in
Scripts to be executed when they are called, or when an event is triggered, are placed in functions.
Put your functions in the head section, this way they are all in one place, and they do not interfere with page content.
Example
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Scripts in
If you don't want your script to be placed inside a function, or if your script should write page content, it should be placed in the body section.
Example
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Scripts in and
You can place an unlimited number of scripts in your document, so you can have scripts in both the body and the head section.
Example
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JS Basic
JS HOME
JS Introduction JS How To JS Where To JS Statements JS Comments JS Variables JS Operators JS Comparisons JS If...Else JS Switch JS Popup Boxes JS Functions JS For Loop JS While Loop JS Break Loops JS For...In JS Events JS Try...Catch JS Throw JS Special Text JS Guidelines
JS Objects
JS Objects Intro JS String JS Date JS Array JS Boolean JS Math JS RegExp
JS Advanced
JS Browser JS Cookies JS Validation JS Animation JS Image Maps JS Timing JS Create Object JS Summary
JS Examples
JS Examples JS Objects Examples JS Browser Examples JS HTML DOM Examples JS Quiz JS Exam
JS References
JavaScript Objects HTML DOM Objects
JavaScript Statements
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JavaScript is a sequence of statements to be executed by the browser.
JavaScript is Case Sensitive
Unlike HTML, JavaScript is case sensitive - therefore watch your capitalization closely when you write JavaScript statements, create or call variables, objects and functions.
JavaScript Statements
A JavaScript statement is a command to a browser. The purpose of the command is to tell the browser what to do.
This JavaScript statement tells the browser to write "Hello Dolly" to the web page:
document.write("Hello Dolly");
It is normal to add a semicolon at the end of each executable statement. Most people think this is a good programming practice, and most often you will see this in JavaScript examples on the web.
The semicolon is optional (according to the JavaScript standard), and the browser is supposed to interpret the end of the line as the end of the statement. Because of this you will often see examples without the semicolon at the end.
Note: Using semicolons makes it possible to write multiple statements on one line.
JavaScript Code
JavaScript code (or just JavaScript) is a sequence of JavaScript statements.
Each statement is executed by the browser in the sequence they are written.
This example will write a heading and two paragraphs to a web page:
Example
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JavaScript Blocks
JavaScript statements can be grouped together in blocks.
Blocks start with a left curly bracket {, and ends with a right curly bracket }.
The purpose of a block is to make the sequence of statements execute together.
This example will write a heading and two paragraphs to a web page:
Example
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The example above is not very useful. It just demonstrates the use of a block. Normally a block is used to group statements together in a function or in a condition (where a group of statements should be executed if a condition is met).
You will learn more about functions and conditions in later chapters.
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JS Basic
JS HOME
JS Introduction JS How To JS Where To JS Statements JS Comments JS Variables JS Operators JS Comparisons JS If...Else JS Switch JS Popup Boxes JS Functions JS For Loop JS While Loop JS Break Loops JS For...In JS Events JS Try...Catch JS Throw JS Special Text JS Guidelines
JS Objects
JS Objects Intro JS String JS Date JS Array JS Boolean JS Math JS RegExp
JS Advanced
JS Browser JS Cookies JS Validation JS Animation JS Image Maps JS Timing JS Create Object JS Summary
JS Examples
JS Examples JS Objects Examples JS Browser Examples JS HTML DOM Examples JS Quiz JS Exam
JS References
JavaScript Objects HTML DOM Objects
JavaScript Comments
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JavaScript comments can be used to make the code more readable.
JavaScript Comments
Comments can be added to explain the JavaScript, or to make the code more readable.
Single line comments start with //.
The following example uses single line comments to explain the code:
Example
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JavaScript Multi-Line Comments
Multi line comments start with /* and end with */.
The following example uses a multi line comment to explain the code:
Example
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Using Comments to Prevent Execution
In the following example the comment is used to prevent the execution of a single code line (can be suitable for debugging):
Example
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In the following example the comment is used to prevent the execution of a code block (can be suitable for debugging):
Example
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Using Comments at the End of a Line
In the following example the comment is placed at the end of a code line:
JS Basic
JS HOME
JS Introduction JS How To JS Where To JS Statements JS Comments JS Variables JS Operators JS Comparisons JS If...Else JS Switch JS Popup Boxes JS Functions JS For Loop JS While Loop JS Break Loops JS For...In JS Events JS Try...Catch JS Throw JS Special Text JS Guidelines
JS Objects
JS Objects Intro JS String JS Date JS Array JS Boolean JS Math JS RegExp
JS Advanced
JS Browser JS Cookies JS Validation JS Animation JS Image Maps JS Timing JS Create Object JS Summary
JS Examples
JS Examples JS Objects Examples JS Browser Examples JS HTML DOM Examples JS Quiz JS Exam
JS References
JavaScript Objects HTML DOM Objects
JavaScript Variables
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Variables are "containers" for storing information.
Do You Remember Algebra From School?
Do you remember algebra from school? x=5, y=6, z=x+y
Do you remember that a letter (like x) could be used to hold a value (like 5), and that you could use the information above to calculate the value of z to be 11?
These letters are called variables , and variables can be used to hold values (x=5) or expressions (z=x+y).
JavaScript Variables
As with algebra, JavaScript variables are used to hold values or expressions.
A variable can have a short name, like x, or a more descriptive name, like carname.
Rules for JavaScript variable names:
- Variable names are case sensitive (y and Y are two different variables)
- Variable names must begin with a letter or the underscore character
Note: Because JavaScript is case-sensitive, variable names are case-sensitive.
Example
A variable's value can change during the execution of a script. You can refer to a variable by its name to display or change its value.
This example will show you how
Declaring (Creating) JavaScript Variables
Creating variables in JavaScript is most often referred to as "declaring" variables.
You can declare JavaScript variables with the var statement :
var x;
var carname;
After the declaration shown above, the variables are empty (they have no values yet).
However, you can also assign values to the variables when you declare them:
var x=5;
var carname="Volvo";
After the execution of the statements above, the variable x will hold the value 5 , and carname will hold the value Volvo.
Note: When you assign a text value to a variable, use quotes around the value.
Assigning Values to Undeclared JavaScript Variables
If you assign values to variables that have not yet been declared, the variables will automatically be declared.
These statements:
x=5;
carname="Volvo";
have the same effect as:
var x=5;
var carname="Volvo";
Redeclaring JavaScript Variables
If you redeclare a JavaScript variable, it will not lose its original value.
var x=5;
var x;
After the execution of the statements above, the variable x will still have the value of 5. The value of x is not reset (or cleared) when you redeclare it.
JavaScript Arithmetic
As with algebra, you can do arithmetic operations with JavaScript variables:
y=x-5;
z=y+5;
You will learn more about the operators that can be used in the next chapter of this tutorial.
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Example
x=5+5;
document.write(x);
x="5"+"5";
document.write(x);
x=5+"5";
document.write(x);
x="5"+5;
document.write(x);
Try it yourself »
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JS Basic
JS HOME
JS Introduction JS How To JS Where To JS Statements JS Comments JS Variables JS Operators JS Comparisons JS If...Else JS Switch JS Popup Boxes JS Functions JS For Loop JS While Loop JS Break Loops JS For...In JS Events JS Try...Catch JS Throw JS Special Text JS Guidelines
JS Objects
JS Objects Intro JS String JS Date JS Array JS Boolean JS Math JS RegExp
JS Advanced
JS Browser JS Cookies JS Validation JS Animation JS Image Maps JS Timing JS Create Object JS Summary
JS Examples
JS Examples JS Objects Examples JS Browser Examples JS HTML DOM Examples JS Quiz JS Exam
JS References
JavaScript Objects HTML DOM Objects
JavaScript Comparison and Logical Operators
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Comparison and Logical operators are used to test for true or false.
Comparison Operators
Comparison operators are used in logical statements to determine equality or difference between variables or values.
Given that x=5 , the table below explains the comparison operators:
Operator Description Example == is equal to x==8 is false === is exactly equal to (value and type) x===5 is true x==="5" is false != is not equal x!=8 is true > is greater than x>8 is false < is less than x<8 is true >= is greater than or equal to x>=8 is false <= is less than or equal to x<=8 is true
How Can it be Used
Comparison operators can be used in conditional statements to compare values and take action depending on the result:
if (age<18) document.write("Too young");
You will learn more about the use of conditional statements in the next chapter of this tutorial.
Logical Operators
Logical operators are used to determine the logic between variables or values.
Given that x=6 and y=3 , the table below explains the logical operators:
Operator Description Example && and (x < 10 && y > 1) is true || or (x==5 || y==5) is false ! not !(x==y) is true
Conditional Operator
JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.
Syntax
variablename=(condition)?value1:value
Example
greeting=(visitor=="PRES")?"Dear President ":"Dear ";
If the variable visitor has the value of "PRES", then the variable greeting will be assigned the value "Dear President " else it will be assigned "Dear".
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document.write("Good day!");
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If...else if...else Statement
Use the if....else if...else statement to select one of several blocks of code to be executed.
Syntax
if ( condition1 )
code to be executed if condition1 is true
else if ( condition2 )
code to be executed if condition2 is true
else
code to be executed if condition1 and condition2 are not true
Example
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More Examples
Random link This example demonstrates a link, when you click on the link it will take you to W3Schools.com OR to RefsnesData.no. There is a 50% chance for each of them.
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JS Basic
JS HOME
JS Introduction JS How To JS Where To JS Statements JS Comments JS Variables JS Operators JS Comparisons JS If...Else JS Switch JS Popup Boxes JS Functions JS For Loop JS While Loop JS Break Loops JS For...In JS Events JS Try...Catch JS Throw JS Special Text JS Guidelines
JS Objects
JS Objects Intro JS String JS Date JS Array JS Boolean JS Math JS RegExp
JS Advanced
JS Browser JS Cookies JS Validation JS Animation JS Image Maps JS Timing JS Create Object JS Summary
JS Examples
JS Examples JS Objects Examples JS Browser Examples JS HTML DOM Examples JS Quiz JS Exam
JS References
JavaScript Objects HTML DOM Objects
JavaScript Switch Statement
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Conditional statements are used to perform different actions based on different
conditions.
The JavaScript Switch Statement
Use the switch statement to select one of many blocks of code to be executed.
Syntax
switch(n)
case 1:
execute code block 1
break;
case 2:
execute code block 2
break;
default:
code to be executed if n is different from case 1 and 2
This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically.
Example
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If the user clicks "OK" the box returns the input value. If the user clicks "Cancel" the box returns null.
Syntax
prompt("sometext","defaultvalue");
Example
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More Examples
Alert box with line breaks
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JS Basic
JS HOME
JS Introduction JS How To JS Where To JS Statements JS Comments JS Variables JS Operators JS Comparisons JS If...Else JS Switch JS Popup Boxes JS Functions JS For Loop JS While Loop JS Break Loops JS For...In JS Events JS Try...Catch JS Throw JS Special Text JS Guidelines
JS Objects
JS Objects Intro JS String JS Date JS Array JS Boolean JS Math JS RegExp
JS Advanced
JS Browser JS Cookies JS Validation JS Animation JS Image Maps JS Timing JS Create Object JS Summary
JS Examples
JS Examples JS Objects Examples JS Browser Examples JS HTML DOM Examples JS Quiz JS Exam
JS References
JavaScript Objects HTML DOM Objects
JavaScript Functions
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A function will be executed by an event or by a call to the function.
JavaScript Functions
To keep the browser from executing a script when the page loads, you can put your script into a function.
A function contains code that will be executed by an event or by a call to the function.
You may call a function from anywhere within a page (or even from other pages if the function is embedded in an external .js file).
Functions can be defined both in the and in the section of a document. However, to assure that a function is read/loaded by the browser before it is called, it could be wise to put functions in the section.
How to Define a Function
Syntax
function functionname ( var1,var2,...,varX )
some code
The parameters var1, var2, etc. are variables or values passed into the function. The { and the } defines the start and end of the function.
Note: A function with no parameters must include the parentheses () after the function name.
Note: Do not forget about the importance of capitals in JavaScript! The word function must be written in lowercase letters, otherwise a JavaScript error occurs! Also note that you must call a function with the exact same capitals as in the function name.
JavaScript Function Example
Example
Try it yourself »
If the line: alert("Hello world!!") in the example above had not been put within a function, it would have been executed as soon as the line was loaded. Now, the script is not executed before a user hits the input button. The function displaymessage() will be executed if the input button is clicked.
You will learn more about JavaScript events in the JS Events chapter.
The return Statement
The return statement is used to specify the value that is returned from the function.
So, functions that are going to return a value must use the return statement.
The example below returns the product of two numbers (a and b):
Example
