Load external Javascript on function call

Question

I would like to know how to load an external Javascript into my document from a function.

Answer 1

Get it with AJAX and then eval() the code.

Answer 2

This is one way:

function loadDaFun() {
   var script = document.createElement('script');
   script.src = '/path/to/your/script.js';
   var head = document.getElementsByTagName("head")[0];
   head.appendChild(script);
}

Answer 3

The @seth's answer is completely right, but you don't need to leave the inserted script element on the DOM, you can remove it just after it is loaded, and also you might want to know when the inserted script is ready to use, for example you can:

function loadScript(url, completeCallback) {
   var script = document.createElement('script'), done = false,
       head = document.getElementsByTagName("head")[0];
   script.src = url;
   script.onload = script.onreadystatechange = function(){
     if ( !done && (!this.readyState ||
          this.readyState == "loaded" || this.readyState == "complete") ) {
       done = true;
       completeCallback();

      // IE memory leak
      script.onload = script.onreadystatechange = null;
      head.removeChild( script );
    }
  };
  head.appendChild(script);
}

Usage:

loadScript("http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js",
            function () { alert('jQuery has been loaded.'); });