Is there any chance to find source of javascript alert?

Question

I'm working in a large project that was developed for several years and had tons of code. Recently uninformative alert start to appear. It just says Undefined. I need to find the source of this alert. Is the any chance to make something like "breakpoint on alert"? I want to see the source of this alert. One possibility is to redefine alert function. I tried to make it in firefox without any success.

Answer 1

I'd go with redefining window.alert right at the start of the code for this type of development purposes.

window.alert = function(e){ console.warn( "Alerted: " + e ); }

This will give You a line number for sure. ( Tested on chrome console )

Answer 2

This is an old question, but thought I would help out with a simpler solution. A very easy way in Chrome to find the source is by placing a debug in the console on window.alert:

debug(window.alert)

This will break on alert and take you to the source. In general, using console with debug(fname) will break whenever the function fname is called.