javascript - 在客户端完成并行、异步调用后执行操作

Question

在我的客户端代码中，我并行触发多个异步请求，我想在每个请求完成后调用一个方法。

这是我的代码

_handlePostSubmit() {
    this._clearFailedPostingGraphs();

    _.forEach(this.state.selectedGraphs, (graph) => {
      this.__createPosting(graph.graphType, graph._id, this.state.content, (error, result) => {
        if (error) {
          this._pushFailedPostingGraph(graph, error);
        } else {
          this._pushSuccesfulPostingGraph(graph);
        }
      }, this);
    }, this);
    this.props.onFetchPostings(); <------- should be called when all the 'createPosting' have completed
  },

我怎样才能做到这一点？

Answer 1

and I want to call a method, after each has completed.

我假设您的意思是在所有请求 完成之后。

如果是这样，计算来自异步请求的回调，如果它们等于异步请求的数量，则执行下一步:

_handlePostSubmit() {
  this._clearFailedPostingGraphs();

  var expectedCallbacks = this.state.selectedGraphs.length;
  var callbackCount = 0;

  _.forEach(this.state.selectedGraphs, (graph) => {
    this.__createPosting(graph.graphType, graph._id, this.state.content, (error, result) => {
      if (error) {
        this._pushFailedPostingGraph(graph, error);
      } else {
        this._pushSuccesfulPostingGraph(graph);
      }

      callbackCount++;

      // this is what I moved -- the method you want to call after everything's done
      if (callbackCount >= expectedCallbacks) {
        this.props.onFetchPostings();
      }
    }, this);
  }, this);
},

jQuery 的 .when() 和 Underscore 的 after() 将执行此操作，您无需手动设置计数器变量。