← JavaScript Introduction JavaScript Output →

JS TutorialLesson #3

JavaScript Where To

In HTML, JavaScript code is inserted between and tags.

The Tag

In HTML, JavaScript code is inserted between and tags.

Example

Example Code

html

Try it Yourself

document.getElementById("demo").innerHTML = "My First JavaScript";

Old JavaScript examples may use a type attribute: . > The type attribute is not required. JavaScript is the default scripting language in HTML.

JavaScript Functions and Events

A JavaScript function is a block of JavaScript code, that can be executed when "called" for.

For example, a function can be called when an event occurs, like when the user clicks a button.

You will learn much more about functions and events in later chapters.

JavaScript in or **

You can place any number of scripts in an HTML document.

Scripts can be placed in the , or in the section of an HTML page, or in both.

JavaScript in

In this example, a JavaScript function is placed in the section of an HTML page.

The function is invoked (called) when a button is clicked:

Example

Example Code

html

Try it Yourself

function myFunction() {

  document.getElementById("demo").innerHTML = "Paragraph changed.";

}

## Demo JavaScript in Head

A Paragraph

 Try
it

JavaScript in

In this example, a JavaScript function is placed in the section of an HTML page.

The function is invoked (called) when a button is clicked:

Example

Example Code

html

Try it Yourself

## Demo JavaScript in Body

A Paragraph

   Try
it

function myFunction() {

    document.getElementById("demo").innerHTML = "Paragraph changed.";

}

Placing scripts at the bottom of the element improves the display > speed, because script interpretation slows down the display.

External JavaScript

Scripts can also be placed in external files:

External file: myScript.js

Example Code

javascript

Try it Yourself

function myFunction() {

  document.getElementById("demo").innerHTML = "Paragraph changed.";

}

External scripts are practical when the same code is used in many different web pages.

JavaScript files have the file extension .js.

To use an external script, put the name of the script file in the src (source) attribute of a tag:

Example

Example Code

html

Try it Yourself

You can place an external script reference in or as you like.

The script will behave as if it was located exactly where the tag is located.

External scripts cannot contain tags.

External JavaScript Advantages

Placing scripts in external files has some advantages:

It separates HTML and code
It makes HTML and JavaScript easier to read and maintain
Cached JavaScript files can speed up page loads

To add several script files to one page - use several script tags:

Example

Example Code

html

Try it Yourself

External References

An external script can be referenced in 3 different ways:

With a full URL (a full web address)
With a file path (like /js/)
Without any path

<script src="myScript1.js"></script>

<script src="myScript2.js"></script>

Previous: JavaScript Introduction Next: JavaScript Output