JavaScript Can Change HTML Content
One of many JavaScript HTML methods is getElementById().
The example below \”finds\” an HTML element (with id=\”demo\”), and changes the element content (innerHTML) to \”Hello JavaScript\”:
document.getElementById("demo").innerHTML = "Hello JavaScript";JavaScript accepts both double and single quotes:
document.getElementById('demo').innerHTML = 'Hello JavaScript';The script Tag
In HTML, JavaScript code is inserted between <script> and </script> tags.
<script>
document.getElementById("demo").innerHTML = "My First JavaScript";
</script>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 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.
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>
<h2>Demo JavaScript in Head</h2>
<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:
<!DOCTYPE html>
<html>
<body>
<h2>Demo JavaScript in Body</h2>
<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>External JavaScript
Scripts can also be placed in external files:
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 <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.