不懂onload事件处理多个事件的代码解释一下

addOnload(initOne)
addOnload(initTwo)
addOnload(initThree)
function addOnload(newFunction) {

var oldOnload = window.onload;

if (typeof oldOnload == "function") {
window.onload = function() {
oldOnload();
newFunction();
}
}
else {
window.onload = newFunction;
}
}