On page load

This article is for XUL/JavaScript developers who want to have custom code executed each time a new page is loaded in browser/mail. If you need finer control over custom code execution—for example, as documents are loading or when tabs are switched—see Progress Listeners.

Progress listeners allow extensions to be notified of events associated with documents loading in the browser and with tab switching events. Progress listeners implement the nsIWebProgressListener interface.

Creating an overlay

First, you need to create an overlay to one (or more, depending on which applications you target) of the following XUL documents:

Attaching a script

Attach a script to your overlay (see "Attaching a Script to an Overlay") that adds a load event listener to appcontent element (browsers) or messagepane (mail):

window.addEventListener("load", function load(event){
    window.removeEventListener("load", load, false); //remove listener, no longer needed
    myExtension.init();  
},false);
var myExtension = {
  init: function() {
    var appcontent = document.getElementById("appcontent");   // browser
    if(appcontent){
      appcontent.addEventListener("DOMContentLoaded", myExtension.onPageLoad, true);
    }
    var messagepane = document.getElementById("messagepane"); // mail
    if(messagepane){
      messagepane.addEventListener("load", function(event) { myExtension.onPageLoad(event); }, 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.
    if(doc.location.href.search("forum") > -1)
      alert("a forum page is loaded");
    // add event listener for page unload 
    aEvent.originalTarget.defaultView.addEventListener("unload", function(event){ myExtension.onPageUnload(event); }, true);
  },
  onPageUnload: function(aEvent) {
    // do something
  }
};

Current Firefox trunk nightlies will fire the onPageLoad function for not only documents, but xul:images (favicons in tabbrowser). If you only want to handle documents, ensure aEvent.originalTarget.nodeName == "#document" .

If you are running code on a page load it is likely you would want to run some cleanup code on page unload. To attach to the unload event in above example you can use the "pagehide" event like this:

appcontent.addEventListener("pagehide", myExtension.onPageUnload, false);

for appcontent and similarly for messagepane

messagepane.addEventListener("pagehide", myExtension.onPageUnload, false);

and add your code to onPageUnload method.

Basic onPageLoad for a browser window

var myExtension = {
    init: function() {
        // The event can be DOMContentLoaded, pageshow, pagehide, load or unload.
        if(gBrowser) gBrowser.addEventListener("DOMContentLoaded", this.onPageLoad, false);
    },
    onPageLoad: function(aEvent) {
        var doc = aEvent.originalTarget; // doc is document that triggered the event
        var win = doc.defaultView; // win is the window for the doc
        // test desired conditions and do something
        // if (doc.nodeName != "#document") return; // only documents
        // if (win != win.top) return; //only top window.
        // if (win.frameElement) return; // skip iframes/frames
        alert("page is loaded \n" +doc.location.href);
    }
}
window.addEventListener("load", function load(event){
    window.removeEventListener("load", load, false); //remove listener, no longer needed
    myExtension.init();  
},false);

References

• If you need to have a more complicated listener (not just onload), use Progress Listeners.

See also

• DOMContentLoaded event in Listening to events: Simple DOM events