onload function

gistfile1.js

function addOnload(newFunction) {
    var oldOnload = window.onload;
    if(typeof oldOnload === "function") {
        alert("OldOnload is not null");
        window.onload = function() {
            if (oldOnload) {
                alert("OLD found, Let do OLD");
                oldOnload();
            }
            alert("Do new function");
            newFunction();
        };
    } else {
        alert("First run,set oldOnload");
        window.onload = newFunction;
    }
}