function loadJavaScriptOnDemand(src, callback) {
var script = document.createElement('script');
script.src = src;
document.getElementsByTagName('head')[0].appendChild(script);
script.onreadystatechange = function() {
if (script.readyState == 4 || script.readyState == "complete") {
if (typeof callback == "function") {
callback();
}
callback = null;
}
}
}
Above function you can call as following.
loadJavaScriptOnDemand(‘path/to/your/javascript’,function(){alert(‘JavaScript loaded’)});