Node.js -> TypeError：无法读取上下文中未定义的属性“then”

Question

I have a node.js file that is calling an async function and I keep getting a TypeError where property of "then" cannot be undefined at context.

async.js

if ( typeof window === 'undefined' ) {
  require('../../app/async');
  var expect = require('chai').expect;
}

describe('async behavior', function() {
  it('you should understand how to use promises to handle asynchronicity', function(done) {
    var flag = false;
    var finished = 0;
    var total = 2;

    function finish(_done) {
      if (++finished === total) { _done(); }
    }

    // This is where the error occurs
    asyncAnswers.async(true).then(function(result) {
      flag = result;
      expect(flag).to.eql(true);
      finish(done);
    });

    asyncAnswers.async('success').then(function(result) {
      flag = result;
      expect(flag).to.eql('success');
      finish(done);
    });

    expect(flag).to.eql(false);

    });

app/async

exports = typeof window === 'undefined' ? global : window;

exports.asyncAnswers = {
  async: function(value) {

 },

 manipulateRemoteData: function(url) {

 }
};

Any help would be greatly appreciated!

Answer 1

Your async function in app/async needs to return a Promise object. Right now, it isn't returning anything.

Answer 2

You should change your async function in something like this using a Promise object:

exports = typeof window === 'undefined' ? global : window;

exports.asyncAnswers = {
  async: function(value) {
    return new Promise(function (resolve, reject){
      // DO YOUR STUFF HERE
      // use resolve to complete the promise successfully
      resolve(returnValueOrObject);
      // use reject to complete the promise with an error
      reject(errorGenerated);
    });
  },

  manipulateRemoteData: function(url) {

  }
};