function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      oldonload();
      func();
    }
  }
}

http://simonwillison.net/2004/May/26/addLoadEvent/

Description: Execute different functions when the page loads in a better way than default onload JS event. Include it in the end of the JS document.
Arguments: Name of the function that you want to execute when the page loads.
Author: Simon Willison

addLoadEvent function

function

JavaScript