There is no window.onsave event that I could find. However, you COULD listen for the ctrl+s keystroke which is easily intercepted.
var isCtrl = false;
document.onkeyup=function(e){
if(e.keyCode == 17) isCtrl=false;
}
document.onkeydown=function(e){
if(e.keyCode == 17) isCtrl=true;
if(e.keyCode == 83 && isCtrl == true) {
//run code for CTRL+S -- ie, save!
return false;
}
}
Code courtesy of: How do I capture a CTRL-S without jQuery or any other library?