JS Proxy Pattern

Question

I use this code to override the window.alert function. The function replaces breaks by \r\n. It works fine in Firefox, but ofcourse not in IE. Im getting the error: Property or method not supported.

(function() {
 var proxied = window.alert;
 window.alert = function(txt) {
 txt = txt.replace(/<br>/g, "\r\n");
 return proxied.apply(this, arguments);
 };
})();

Please help me find the solution! Thank you

• Abhinav Sarkar: In which line do you get the error?

Answer 1

I would do this, in case window.alert is not a "real" function in IE:

(function() {
 var proxied = window.alert;
 window.alert = function(txt) {
 txt = txt.replace(/<br>/g, "\r\n");
 return proxied(txt);
 };
})();

Sorry, untested, Does it work?

• Bram Verstraten: Thank you for your reply. Now the error is gone, and the alert is showing, but breaks are not replaced. It's still working fine in FF though. Any ideas?
• Bram Verstraten: I changed the location of the code in my script and it's working fine now in both IE and FF. Thank you Victor! @Tim, I appriciate your input, and I know it's not the best way to do it, but otherwise I had to replace the alert function in my scripts to a custom made alert function. Knowing there are over 1000 scripts on my website, that's just not doable.

Answer 2

This would be fine for native JavaScript functions but is highly dangerous with methods of host objects such as window. Host objects are not subject to the normal rules of native JavaScript objects, and can (and do) behave largely as they please, often differently in different browsers. Therefore I strongly recommend not pursuing this idea for window.alert or any other host methods.