Autorun Javascript

On page loaded:

function autorun() {
    // Your code here
}
if (window.addEventListener) window.addEventListener("load", autorun, false);
else if (window.attachEvent) window.attachEvent("onload", autorun);
else window.onload = autorun;

On DOM ready:

if (document.addEventListener) document.addEventListener("DOMContentLoaded", autorun, false);
else if (document.attachEvent) document.attachEvent("onreadystatechange", autorun);
else window.onload = autorun;