Creating widget using javascript and PHP

I am working on creating widget using PHP and Javascript. In a widget, you get a small code like this:

<div id="wd_id"></div><script type="text/javascript" src="http://localhost/hasanResearch/php/widgets/widget.js"></script><script type="text/javascript">init_widget()</script>

You need to paste this code in your html file. This piece of code calls a function init_widget() in widget.js. The script inside widget.js is somethis like this:

function init_widget(params){
    document.getElementById("wd_id").innerHTML='html code goes here';
}

This will load the entire html page. In my case, the JS file and all the files are located on server. I have copied the code in my local. When I open the html file in browser, it shows error as Uncaught ReferenceError: init_widget is not defined.

Do anyone have clue, why it is happening?