xr 是 XMLHttpRequest 的超简单封装，并返回 ES6 Promise。

特性

• Returns ES6 promises.
• Has query parameter generation.
• Supports events.

示例代码：

xr.get('/api/items', {take: 5})    .then(res => console.log(res.data));     xr.post('/api/item', {name: 'hello'})    .then(res => console.log("new item", res.data));     xr({    method: xr.Methods.GET,    url: '/api/items',    params: {take: 5},    events: {      progress: (xhr, xhrProgressEvent) => {        console.log("xhr", xhr);        console.log("progress", xhrProgressEvent);      }    }  });

项目主页：http://www.open-open.com/lib/view/home/1425347214415