How to Load Scripts Synchronously in JavaScript: Why and When?

Synchronous Loading of Script Files Using document.createElement("script")

Loading external scripts asynchronously ensures that page rendering is not blocked while the scripts are being retrieved and parsed. However, there may be use cases where you need to load a script file synchronously and utilize it immediately.

The code snippet attempts to synchronously load a script file and invoke a function from it. However, it encounters a timing issue as the script hasn't yet been loaded and executed when the function is called.

Resolving this issue involves recognizing that loading scripts asynchronously is the standard approach. However, in certain specific scenarios, you may need to control the loading process manually.

Custom Script Loading Function

To improve the script loading process, you could create a custom function that incorporates an "onload" handler to the created <script> element. Once the script is successfully loaded, the "onload" function will be triggered, signaling that the script has been parsed and is ready to be used.</script>

<code class="js">function Include(src) {
  var script = document.createElement('script');
  script.onload = function() {
    console.log("Script " + src + " has been loaded.");
  };
  script.src = src;
  document.getElementsByTagName('head')[0].appendChild(script);
}</code>

Example Usage

With this custom function, you can easily include and use scripts in a sequential manner.

<code class="js">Include('my1.js');
Include('my2.js');

myFunc1('blarg');
myFunc2('bleet');</code>

Limitations

Note that synchronous script loading may not be desirable in all situations. Excessive usage of synchronous scripts can slow down page rendering and hinder the user experience. It's generally recommended to optimize script loading for asynchronous execution to minimize performance impact.

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