Question

Some context: I’m making an add-on for firefox. In firefox add-ons, js scripts can be attached to a webpage at certain events (content scripts). In those scripts I’d like to use the prototype of XMLHttpRequest.

Is it possible to access the prototypes of the available classes in javascript? For example: XMLHttpRequest.toString() returns [object XMLHttpRequest], while XMLHttpRequest.prototype is null. Am I doing anything wrong, or isn’t it possible to use prototypes in those scripts?

Answer 1

Yes, you must be doing something wrong. I tried with a minimal SDK-based extension, the main.js file being:

var pageMod = require("page-mod");
pageMod.PageMod({
  include: "*.google.com",
  contentScriptWhen: "end",
  contentScript: 'throw "XMLHttpRequest.prototype = " + XMLHttpRequest.prototype'
});

When I load google.com I see the following message in the Error Console:

XMLHttpRequest.prototype = [object XMLHttpRequestPrototype]

So XMLHttpRequest.prototype is definitely not null.