var QUERY = 'puppies';

var kittenGenerator = {

searchOnFlickr_: 'https://secure.flickr.com/services/rest/?',


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

showPhotos_: function (e) {
var kittens = e.target.responseXML.querySelectorAll('photo');
for (var i = 0; i < kittens.length; i++) {
var img = document.createElement('img');
img.src = this.constructKittenURL_(kittens[i]);
img.setAttribute('alt', kittens[i].getAttribute('title'));
document.body.appendChild(img);
}
},

constructKittenURL_: function (photo) {
return "http://farm" + photo.getAttribute("farm") +
".static.flickr.com/" + photo.getAttribute("server") +
"/" + photo.getAttribute("id") +
"_" + photo.getAttribute("secret") +
"_s.jpg";
}
};

// Run our kitten generation script as soon as the document's DOM is ready.
document.addEventListener('DOMContentLoaded', function () {
kittenGenerator.requestKittens();
});


是谷歌的js代码，太长了，做了删减。能否先解释一下大概语法，然后告诉我哪里可以找到，谢谢。我在w3cschool 上面找不到这语法。