Question

I am following google chrome’s extension development guide here:
http://developer.chrome.com/extensions/getstarted.html

In line 41 of this file: http://sprunge.us/NFjZ

requestKittens: function() {
  var req = new XMLHttpRequest();
  req.open("GET", this.searchOnFlickr_, true);
  req.onload = this.showPhotos_.bind(this);
  req.send(null);
},

, they used the bind function like this
this.showPhotos_.bind(this); and without this binding, the example extension will not work. I tested in the showPhotos_ method and verified that “this” is just the kittenGenerator object. Since showPhotos_ is just a method of that object, this should be implicitly done, so why is this binding necessary anyway?

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Note that google’s example will not work due to a spelling mistake in the popup.js file.
To correct it, change “kittensOnFlickr_” into “searchOnFlickr_”.

Answer 1

Without the binding showPhotos_ when called from req.onload, the this will be req not kittenGenerator.