How to Include a JavaScript File in another JavaScript File

Answer: Use the `export` and `import` Statement

Since ECMAScript 6 (or ES6) you can use the export or import statement in a JavaScript file to export or import variables, functions, classes or any other entity to/from other JS files.

For example, let's suppose you've two JavaScript files named "main.js" and "app.js" and you want to export some variables and functions from "main.js" to "app.js". Then in "main.js" file you need to write the export statement (line no-9) as shown in the following example:

Example

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let msg = "Hello World!";
const PI = 3.14; 
 
function addNumbers(a, b){
    return a + b;
}
 
// Exporting variables and functions
export { msg, PI, addNumbers };

And in "app.js" file you need to write the import statement (line no-1) as shown here:

Example

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import { msg, PI, addNumbers } from './main.js';
 
console.log(msg); // Prints: Hello World!
console.log(PI); // Prints: 3.14
console.log(addNumbers(5, 16)); // Prints: 21

Alternatively, you can use the jQuery getScript() method to load a JS file from the server, then execute it with a sigle line of code. Let's suppose you have a JS file "test.js" with the following code.

Example

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// Defining variables
var str = "Hi there!";
var num = 15;
 
// Defining a function
function multiplyNumbers(a, b){
    return a * b;
}

Now you can load this "test.js" file in your script using the getScript() method, like this:

Example

Try this code »

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery Load JS File Demo</title>
<script src="https://code.jquery.com/jquery-3.5.1.min.js"></script>
</head>
<body>
    <script>
    var url = "test.js";
    
    $.getScript(url, function(){
        $(document).ready(function(){
            console.log(str); // Prints: Hi there!
            console.log(num); // Prints: 15
            console.log(multiplyNumbers(4, 25)); // Prints: 100
        });
    });
    </script> 
</body>
</html>

See the tutorial on JavaScript ES6 features to learn about the new features introduced in ES6.