code: function startBuild(buildConf, clear) {
      // init build manager
      let buildManager = BuildManager.create(buildConf.appType, buildConf);
  
      if (clear) {
          buildManager.clear();
      }
  
      startDevServer(buildConf, buildManager);
      let doneHandler = function () {
          startFileChangeMonitor(buildConf, buildManager);
      };
  
      // run build
      return runBuild(buildConf, buildManager).then(
          doneHandler,
          doneHandler
      );
  }
docs: Start to build small application code to native small application code.
  
  @param {Object} buildConf the config to build
  @param {boolean} clear whether clear the old build output before start build
  @return {Promise}