Include JS File from JS

function loadScript(url, callback)
{
    // adding the script tag to the head as suggested before
   var head= document.getElementsByTagName('head')[0];
   var script= document.createElement('script');
   script.type= 'text/javascript';
   script.src= url;

   // then bind the event to the callback function 
   // there are several events for cross browser compatibility
   script.onreadystatechange = callback;
   script.onload = callback

   // fire the loading
   head.appendChild(script);
}

loadScript("my_lovely_script.js", myPrettyCode);
Alternatively, use
$.getScript("my_lovely_script.js", function(){


   alert("Script loaded and executed.");
   // here you can use anything you defined in the loaded script

});