❮ HTML tag
Example
Point to an external JavaScript file:
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Definition and Usage
The src attribute specifies the URL of an external
script file.
If you want to run the same JavaScript on several pages in a web site, you should create an external JavaScript file, instead of writing the same script over and over again. Save the script file with a .js extension, and then refer to it using the src attribute in the
tag.
Note: The external script file cannot contain the
tag.
Note: Point to the external script file exactly where you would have written the script.
Browser Support
| src | Yes | Yes | Yes | Yes | Yes |
Syntax
Attribute Values
| URL | The URL of the external script file. Possible values:
|
❮ HTML tag
The Tag
In HTML, JavaScript code is inserted between and tags.
Example
document.getElementById["demo"].innerHTML = "My First JavaScript";
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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
function myFunction[] {
document.getElementById["demo"].innerHTML
= "Paragraph changed.";
}
Demo JavaScript in Head
A Paragraph
Try it
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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
Demo JavaScript in Body
A Paragraph
Try it
function myFunction[] {
document.getElementById["demo"].innerHTML = "Paragraph changed.";
}
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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
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:
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
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
This example uses a full URL to link to myScript.js:
Example
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This example uses a file path to link to myScript.js:
This example uses no path to link to myScript.js:
You can read more about file paths in the chapter HTML File Paths.