JavaScript Tags
JavaScript Where To
In HTML, JavaScript code is inserted between <script> and </script>
document.getElementById("demo").innerHTML = "My First JavaScript";
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.
JavaScript in Placement
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.
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:.
<!DOCTYPE html>
<html>
<head>
<script>
function myFunction() {
document.getElementById("demo").innerHTML = "Paragraph changed.";
}
</script>
</head>
<body>
<h1>A Web Page</h1>
<p id="demo">A Paragraph</p>
<button type="button" onclick="myFunction()">Try i</button>
</body>
</html>
JavaScript in <body>
In this example, a JavaScript function is placed in the section of an HTML page.
Placing scripts at the bottom of the element improves the display speed, because script interpretation slows down the display.
<!DOCTYPE html>
<html>
<body>
<h1>A Web Page</h1>
<p id="demo">A Paragraph</p>
<button type="button" onclick="myFunction()">Try i</button>
<script>
function myFunction() {
document.getElementById("demo").innerHTML = "Paragraph changed.";
}
</script>
</body>
</html>
External JavaScript
Scripts can also be placed in external files. JavaScript files have the file extension .js. External scripts are practical when the same code is used in many different web pages.
To use an external script, put the name of the script file in the src (source) attribute of a <script> tag:
<script src="myScript.js"> </script>
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.
External scripts cannot contain <script> 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
- it enable us to add several script files to one page - use several script tags:
- Cached JavaScript files can speed up page loads
<script src="myScript1.js.js"> </script>
<script src="myScript2.js.js"> </script>
External References
External scripts can be referenced with a full URL or with a path relative to the current web page.
<script src="https://www.w3schools.com/js/myScript1.js"> </script>
