Passing JavaScript Parameters via Calling URL

Iterate through all <script> elements using getElementsByTagName. Find the one which identifies your script (e.g. by looking for domain.com/widget.js) by examining the src attribute. Extract the query string from the src attribute.

Example:

function getScriptQuery(identifier) {
 var scripts = document.getElementsByTagName('script'),
     i, curScript;

 for (i = 0; i < scripts.length; ++i) {
  curScript = scripts[i];

  if (curScript.src.match(identifier)) {
   return (curScript.src.match(/\?.*/) || [undefined])[0];
  }
 }
}

alert(getScriptQuery('widget.js'));

There are two common alternatives to solving your original problem of passing data to the script.

You can reference a known global variable in your script and have the calling HTML define that variable:

<script type="text/javascript">var MyWidgetData={foo:'bar'};</script>
<script src="http://my.widgeteer.net/widget.js"></script>

// widget.js:

alert(MyWidgetData.foo);

You can also wrap your script as a named function and have calling HTML call that function:

<script src="http://my.widgeteer.net/widget.js"></script>
<script type="text/javascript">MyWidget({foo:'bar'});</script>

// widget.js:

function MyWidget(data) {
    alert(data.foo);
}