JavaScript event binding and in-depth

A Issues with traditional event bindings

To solve the coverage problem, we can solve it this way:
Window.onload = function () {//The first event to be executed will be overwritten
Alert (1);
};
if (typeof window.onload = = ' function ') {//Before judging if there is window.onload
var saved = null; Create a Save
saved = window.onload; Save the previous window.onload.
}
Window.onload = function () {//FINAL one to execute event
if (saved) saved (); Perform a previous event
Alert (2); Code to execute this event
};

JavaScript event binding and in-depth