Debugging autoproxy (PAC) javascript with alert()?

Question

I am writing a custom .pac script for use with Firefox. Following numerous examples I've seen, I intersperse alert()s in order to debug it, but no alerts popup, even though the script is clearly being invoked. (I am clicking "Reload" in the "Connection settings" after each change to my script. I have even tried restarting Firefox.)

Are alerts supposed to work from PAC scripts? Maybe this is an IE-only feature?

Answer 1

http://mxr.mozilla.org/mozilla-central/source/netwerk/base/src/nsProxyAutoConfig.js

The alert function is added to the sandbox:

80         // add predefined functions to pac
81         this._sandBox.importFunction(myIpAddress);
82         this._sandBox.importFunction(dnsResolve);
83         this._sandBox.importFunction(proxyAlert, "alert");

And the mapped function calls dump, which goes to the Error Console:

108 function proxyAlert(msg) {
109     msg = XPCSafeJSObjectWrapper(msg);
110     try {
111         // It would appear that the console service is threadsafe.
112         var cns = Components.classes["@mozilla.org/consoleservice;1"]
113                             .getService(Components.interfaces.nsIConsoleService);
114         cns.logStringMessage("PAC-alert: "+msg);
115     } catch (e) {
116         dump("PAC: proxyAlert ERROR: "+e+"\n");
117     }

Answer 2

1. Use alert function in your .pac file.

2. • In Firefox Browser:

     Tools -> Web Developer -> Browser Console (Ctrl+Shift+J) [This is not Web Console!!] -> Filter output: PAC-alert

   • In Chrome Browser:

     Go to chrome://net-internals/#events -> Search for a record with description: PAC_JAVASCRIPT_ALERT

     ^{(About Chrome, thank this answer)}

---

Sample .pac file:

function FindProxyForURL(url, host) {
    alert("url = " + url + " *** host = " + host + " *** Resolved IP = " + dnsResolve(host));

    return "DIRECT";
}