JavaScript

JavaScript Where To

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JavaScript can be placed in the <body> and the <head> sections of an HTML page.


The <script> Tag

In HTML, JavaScript code must be inserted between <script> and </script> tags.

Example

<script>
document.getElementById(“demo”).innerHTML = “My First JavaScript”;
</script>
Note Older examples may use a type attribute: <script type=”text/javascript”>.
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 “asked” for.

For example, a function can be executed 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 <head> or <body>

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

Scripts can be placed in the <body>, or in the <head> section of an HTML page, or in both.

Note Keeping all code in one place, is always a good habit.

JavaScript in <head>

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

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

Example

<!DOCTYPE html>
<html><head>
<script>
function myFunction() {
document.getElementById(“demo”).innerHTML = “Paragraph changed.”;
}
</script>
</head>

<body>

<h1>My Web Page</h1>

<p id=“demo”>A Paragraph</p>

<button type=“button” onclick=“myFunction()”>Try it</button>

</body>
</html>

JavaScript in <body>

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

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

Example

<!DOCTYPE html>
<html>
<body>

<h1>My Web Page</h1>

<p id=“demo”>A Paragraph</p>

<button type=“button” onclick=“myFunction()”>Try it</button>

<script>
function myFunction() {
document.getElementById(“demo”).innerHTML = “Paragraph changed.”;
}
</script>

</body>
</html>

It is a good idea to place scripts at the bottom of the <body> element.
This can improve page load, because HTML display is not blocked by scripts loading.

External JavaScript

Scripts can also be placed in external files.

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 the <script> tag:

Example

<!DOCTYPE html>
<html>
<body>
<script src=“myScript.js”></script>
</body>
</html>

You can place an external script reference in <head> or <body> as you like.

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

Note External scripts cannot contain <script> tags.

External JavaScript Advantages

Placing JavaScripts 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

JavaScript Introduction

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JavaScript is the most popular programming language in the world.

This page contains some examples of what JavaScript can do.


JavaScript Can Change HTML Content

One of many HTML methods is getElementById().

This example uses the method to “find” an HTML element (with id=”demo”), and changes the element content (innerHTML) to “Hello JavaScript”:

Example

document.getElementById(“demo”).innerHTML = “Hello JavaScript”;

 

 

JavaScript Can Change HTML Styles (CSS)

Changing the style of an HTML element, is a variant of changing an HTML attribute:

Example

document.getElementById(“demo”).style.fontSize = “25px”;

 

 

Did You Know?

Note JavaScript and Java are completely different languages, both in concept and design.
JavaScript was invented by Brendan Eich in 1995, and became an ECMA standard in 1997.
ECMA-262 is the official name. ECMAScript 5 (JavaScript 1.8.5 – July 2010) is the current standard.

 

JavaScript Tutorial

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javascript

JavaScript is the programming language of HTML and the Web.

Programming makes computers do what you want them to do.

JavaScript is easy to learn.

This tutorial will teach you JavaScript from basic to advanced.

Why Study JavaScript?

JavaScript is one of the 3 languages all web developers must learn:

1. HTML to define the content of web pages

2. CSS to specify the layout of web pages

3. JavaScript to program the behavior of web pages

This tutorial is about JavaScript, and how JavaScript works with HTML and CSS.


Learning Speed

In this tutorial, the learning speed is your choice.

Everything is up to you.

If you are struggling, take a break, or reread the material.