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var getJSON = function(url) { var promise = new RSVP.Promise(function(resolve, reject){ var client = new XMLHttpRequest(); client.open("GET", url); client.onreadystatechange = handler; client.responseType = "json"; client.setRequestHeader("Accept", "application/json"); client.send(); function handler() { if (this.readyState === this.DONE) { if (this.status === 200) { resolve(this.response); } else { reject(this); } } }; }); return promise; }; getJSON("/posts.json").then(function(json) { // continue }, function(error) { // handle errors });
One of the really awesome features of Promises/A+ promises are that they can be chained together. In other words, the return value of the first resolve handler will be passed to the second resolve handler.
If you return a regular value, it will be passed, as is, to the next handler.
getJSON("/posts.json").then(function(json) {
return json.post;
}).then(function(post) {
// proceed
});
The really awesome part comes when you return a promise from the first handler:
getJSON("/post/1.json").then(function(post) {
// save off post
return getJSON(post.commentURL);
}).then(function(comments) {
// proceed with access to post and comments
});
转自: https://github.com/tildeio/rsvp.js
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原文地址：http://www.cnblogs.com/xjinza/p/4702637.html
