function request(url, callback) {
  fetch(url, {mode: 'cors', credentials: 'include', headers: new Headers({ 'X-Requested-With': 'XMLHttpRequest' })})
  .then(response => response.text())
  .then(text => {
    console.log(url);
    console.log(text);
    callback(text);
  })
  .catch((e) => console.log(e));
}

var iterator = null;
function getData(src){
  request(src, function(response){
    iterator.next(JSON.parse(response));
  })
}

function getTpl(src){
  request(src, function(response){
    iterator.next(response);
  });
}

// 同步任务
function render(data, tpl){
  for(var i in data) {
    tpl = tpl.replace("${"+i+"}", data[i]);
  }
  return tpl;
}

// 主逻辑
var getArticles = function* (src){
  console.log('begin')
  var data = yield getData(src)
  var tpl = yield getTpl(data.tpl)
  var res = render(data, tpl)
  console.log(res)
}

iterator = getArticles('data.json')
// 开始执行
iterator.next()
// 异步任务模型