如何从Firefox扩展中覆盖JavaScript函数？ [英] How to override JavaScript function from a Firefox extension?

问题描述

我正在尝试拦截对所有页面的document.write调用。通过注入脚本来设置页面内的拦截，如

I am trying to intercept calls to document.write for all pages. Setting up the interception inside the page by injecting a script like

function overrideDocWrite() {
 alert("Override called");
 document.write = function(w) {
  return function(s) {
   alert("special dom");
   w.call(this, wrapString(s));
  };
 }(document.write);
 alert("Override finished");
}

很容易且有效，但我希望我的扩展能够设置截取扩展内部的每个文档对象。我找不到办法做到这一点。我试着听加载事件并在那里设置拦截，但它也失败了。如何从扩展程序挂接对 doc.write 的调用？

Is easy and works, but I would like my extension to setup the interception for each document object from inside the extension. I couldn't find a way to do this. I tried to listen for the "load" event and set up the interception there but it also fails. How do I hook calls to doc.write from an extension?

我取得了一些进展：

var myExtension = {
  init: function() {
    var appcontent = document.getElementById("appcontent"); // browser
    if (appcontent)
      appcontent.addEventListener("DOMContentLoaded", myExtension.onPageLoad,
        true);
  },

  onPageLoad: function(aEvent) {
    var doc = aEvent.originalTarget; // doc is document that triggered "onload" event
    // do something with the loaded page.
    // doc.location is a Location object (see below for a link).
    // You can use it to make your code executed on certain pages only.
    alert("Override called");
    alert(doc);
    alert(doc.write);
    alert(doc.wrappedJSObject);
    alert(doc.wrappedJSObject.write);
    doc.wrappedJSObject.write = function(w) {
      return function(s) {
        alert("special dom");
        w.call(this, "(" + s + ")");
      };
    }(doc.write);
    alert("Override finished");
  }
}

这似乎有效，但DOMContentLoaded是错误的事件因为工作太晚了！是否有较早的事件要听？

This seem to work, but DOMContentLoaded is the wrong event for the job, because it is fired too late! Is there an earlier event to listen to?

推荐答案

问题的重新确定！我得到了答案。以下是示例代码：

Ressurection of the question ! I got the answer. Here is a sample code :

const os    = Components.classes["@mozilla.org/observer-service;1"].getService(Components.interfaces.nsIObserverService);

os.addObserver({
    observe : function(aWindow, aTopic, aData) {
        if (aWindow instanceof Ci.nsIDOMWindow && aTopic == 'content-document-global-created') {
            aWindow.wrappedJSObject.myfunction = function(){
                // Do some stuff . . .
            }
        }
    }
}, 'content-document-global-created', false);

从gecko 2.0开始插入事件document-element的文档也是如此。

The same goes for document with the event document-element-inserted as of gecko 2.0 .

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