Angular2 - Class - XHR

就定义了一个空方法

export class XHR {
  get(url: string): Promise<string> { return null; }
}

要改名字

rename it into TemplateLoader
后来搜到这个东西在用

export class XHRImpl extends XHR {
  get(url: string): Promise<string> {
    var completer: PromiseCompleter < string >= PromiseWrapper.completer();
    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.responseType = 'text';

    xhr.onload = function() {
      // responseText is the old-school way of retrieving response (supported by IE8 & 9)
      // response/responseType properties were introduced in XHR Level2 spec (supported by IE10)
      var response = isPresent(xhr.response) ? xhr.response : xhr.responseText;

      // normalize IE9 bug (http://bugs.jquery.com/ticket/1450)
      var status = xhr.status === 1223 ? 204 : xhr.status;

      // fix status code when it is 0 (0 status is undocumented).
      // Occurs when accessing file resources or on Android 4.1 stock browser
      // while retrieving files from application cache.
      if (status === 0) {
        status = response ? 200 : 0;
      }

      if (200 <= status && status <= 300) {
        completer.resolve(response);
      } else {
        completer.reject(`Failed to load ${url}`, null);
      }
    };

    xhr.onerror = function() { completer.reject(`Failed to load ${url}`, null); };

    xhr.send();
    return completer.promise;
  }
}

其实就是实现了下get方法，返回的是promise所以可以then下去

注： An interface for retrieving documents by URL that the compiler uses to load templates.

看样子可能不是用作普通的API请求用