Debugging autoproxy (PAC) javascript with alert()?

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)}

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Sample .pac file:

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

    return "DIRECT";
}

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     }

Ah Ha! The alert messages are getting logged to the console. I actually prefer that to alert popups anyway.