How to dynamically load JavaScript files: A step-by-step guide

  1. Introduction
  2. Step 1: Create a function to load JavaScript files
  3. Step 2: Call the function to load the JavaScript files
  4. Step 3: Dynamically load multiple JavaScript files
  5. Conclusion


When building websites, it is common to use JavaScript files to add interactivity and dynamic behavior to a webpage. However, as websites become more complex, the number of JavaScript files required may increase, leading to longer load times and slower performance. One way to address this issue is by dynamically loading JavaScript files. In this article, we will provide a step-by-step guide on how to dynamically load JavaScript files.

Step 1: Create a function to load JavaScript files

The first step is to create a function that will load the JavaScript files when called. This can be done using the following code:

function loadScript(url, callback){
    var script = document.createElement("script")
    script.type = "text/javascript";

    if (script.readyState){  //IE
        script.onreadystatechange = function(){
            if (script.readyState == "loaded" ||
                    script.readyState == "complete"){
                script.onreadystatechange = null;
    } else {  //Others
        script.onload = function(){

    script.src = url;

This function creates a new <script> element, sets its type to "text/javascript", and assigns the specified URL to its "src" attribute. It also includes code to handle different browser behaviors for loading scripts.

Step 2: Call the function to load the JavaScript files

Once the function is created, it can be called to load the desired JavaScript files. This can be done using the following code:

loadScript("path/to/your/javascript/file.js", function(){
    // code to run after the script has loaded

This code calls the previously defined loadScript() function, passing in the URL of the JavaScript file to load and a callback function to run after the script has loaded.

Step 3: Dynamically load multiple JavaScript files

To dynamically load multiple JavaScript files, the loadScript() function can be called multiple times with different URLs. Alternatively, an array of URLs can be passed to the function and loaded using a loop. Here is an example:

var scripts = [

var loaded = 0;

function loadAllScripts(){
    loadScript(scripts[loaded], function(){
        if (loaded < scripts.length){


This code creates an array of JavaScript file URLs, defines a variable to keep track of how many scripts have been loaded, and creates a function to load all the scripts in the array. The loadAllScripts() function calls the loadScript() function for each URL, and increments the loaded variable and calls itself recursively until all scripts have been loaded.


Dynamically loading JavaScript files is a useful technique for improving website performance by reducing load times. By creating a function to load scripts and calling it whenever necessary, you can easily load scripts on demand and avoid unnecessary delays. Follow the steps outlined in this guide to start dynamically loading your JavaScript files today.

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