Actually, there is no function you can call to include a JavaScript file within another one. This is the bad news.
The good news is that you can use a trick to accomplish this task. Suppose you have two JavaScript files,
say file1.js and file2.js. You want to include file1.js within file2.js because you want to use file1’s functions.
Here is the code you can use:
//this is file2.js
document.write("<script src='file1.js' type='text/javascript'></script>");
// here you can use functions defined in file1.js
As you can see it suffices “to write” in the browser the code you generally use to include a JavaScript file within an HTML file and you’re done!