Link html to external javascript

How to Link JavaScript to HTML

To link to an external JavaScript file, use where myExternalFile.js is the location of the external file.

The above example links to an external JavaScript file. The location of the JavaScript file is provided as the value for the src attribute. When the HTML file loads, the JavaScript file is also loaded.

Placement of the Tags

External JavaScript files are often linked to from the document but this is not a requirement. You can also place the link within the document element. In fact, more and more developers are linking to their JavaScript files from the bottom of the HTML document (just before the closing tag) for performance reasons. Doing this allows the rest of the HTML page to load without having to wait for external JavaScript resources to be downloaded first.

Embedded JavaScript

This second example uses exactly the same JavaScript as the first example (only the text has changed). The only difference is that the JavaScript is now embedded into the HTML document, as opposed to being located in an external file.

The type Attribute

You can use the type attribute to explictly state the script type. If you omit this attribute the script will be treated as JavaScript. So there is no need to use this attribute if the script is in JavaScript.

If the script is not written in JavaScript, you should use the type attribute to explicitly state the type of script.

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JavaScript Where To

In HTML, JavaScript code is inserted between tags.

Example

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

Demo JavaScript in Head

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

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

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

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

This example uses a file path to link to myScript.js:

Example

This example uses no path to link to myScript.js:

Example

You can read more about file paths in the chapter HTML File Paths.

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How to Link JavaScript to HTML

To link to an external JavaScript file, use where myExternalFile.js is the location of the external file.

The above example links to an external JavaScript file. The location of the JavaScript file is provided as the value for the src attribute. When the HTML file loads, the JavaScript file is also loaded.

Placement of the Tags

External JavaScript files are often linked to from the document but this is not a requirement. You can also place the link within the document element. In fact, more and more developers are linking to their JavaScript files from the bottom of the HTML document (just before the closing tag) for performance reasons. Doing this allows the rest of the HTML page to load without having to wait for external JavaScript resources to be downloaded first.

Embedded JavaScript

This second example uses exactly the same JavaScript as the first example (only the text has changed). The only difference is that the JavaScript is now embedded into the HTML document, as opposed to being located in an external file.

The type Attribute

You can use the type attribute to explictly state the script type. If you omit this attribute the script will be treated as JavaScript. So there is no need to use this attribute if the script is in JavaScript.

If the script is not written in JavaScript, you should use the type attribute to explicitly state the type of script.

Related

Источник