API内部有两个http接口A，B并发调用，如果都在200ms内返回，则合并结果输出，如果B比A慢，且B耗时超过200ms，则丢弃B调用只返回A结果.

apimergecall.js

function apiMergeCall(apis, mainid, timeout, callback){
  var api_count = apis.length, ready_count = 0, rst = {}, is_ret = false, start_time = new Date().getTime(),
      doCallback = function(){
        if (!is_ret && (is_ret = true)) {
          timer && clearTimeout(timer);
          callback(rst);
        }
      },
      chkResult = function(id, ret){
        rst[id] = ret;
        if (++ready_count == api_count || (id == mainid && (new Date().getTime() - start_time > timeout))) {
          doCallback();
        }
      },
      timer = setTimeout(function(){
        timer = null;
        (rst[mainid] !== undefined) && doCallback();
      }, timeout);
      
  apis.forEach(function(api){
    api.exec(chkResult);
  });
}

function Api(id, data){
  this.id = id;
  this.data = data;
}
Api.prototype = {
  exec : function(fn){
    var sleep_time = Math.round(Math.random()*300);
    console.log(this.id + ' ' + sleep_time);
    setTimeout(fn, sleep_time, this.id, this.data);
  }
}

apiMergeCall([new Api('a', 'this is a'), new Api('b', 'this is b')], 'a', 200, function(rst){console.log(rst);});