Where To
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JavaScript Where To
In HTML, JavaScript code is inserted between
<script> and </script> tags. Understanding where to place these scripts is vital for page load performance and execution order.1. The <script> Tag
The
<script> tag tells the browser to interpret the enclosed text as executable code. Old examples might use a type attribute: <script type="text/javascript">. The type attribute is not required. JavaScript is the default scripting language in HTML.<script>
document.getElementById("demo").innerHTML = "My First JavaScript";
</script>2. 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>
Placing scripts at the bottom of the
<body> element improves the display speed, because script interpretation slows down the display.<body>
<p id="demo">A Paragraph</p>
<script>
function myFunction() {
document.getElementById("demo").innerHTML = "Paragraph changed.";
}
</script>
</body>3. External JavaScript
Scripts can also be placed in external files. External files often contain code to be used by 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>Advantages of External JavaScript:
- It separates HTML and code.
- It makes HTML and JavaScript easier to read and maintain.
- Cached JavaScript files can speed up page loads.
Top Interview Questions
?Interview Question
Q:Where is the best place to put JavaScript for performance?
A:
Placing JavaScript at the end of the element is generally best for performance. This allows the HTML content to load and display first without being blocked by script interpretation.
?Interview Question
Q:Can an external JavaScript file contain <script> tags?
A:
No. External JavaScript files (.js) should only contain JavaScript code. They must not include
?Interview Question
Q:What attribute is used to link an external JS file?
A:
The 'src' attribute of the
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