Javascript承诺不等待解决

Question

I thought I had a decent understanding of promises, until I ran into a problem with a simplifed code snippet bellow. I was under the impression that the console.log calls would output first second third , but instead results in second third first .

Can someone explain why the second and third promises are able to continue on without waiting for the first.

var Q = require('q');

(function() {

  var Obj = function() {

    function first() {
      var deferred = Q.defer();

      setTimeout(function() {
        console.log('in the first')
        deferred.resolve();
      }, 200);

      return deferred.promise;
    }

    function second() {
      return Q.fcall(function() {
        console.log('in the second');
      })
    }

    function third() {
      return Q.fcall(function() {
        console.log('in the third');
      })
    }

    return {
      first:  first,
      second: second,
      third:  third
    }
  };

  var obj = Obj();
  obj.first()
    .then(obj.second())
    .then(obj.third());

}());

Answer 1

You shouldn't be invoking the function, but pass the function, like this

  obj.first()
    .then(obj.second)
    .then(obj.third);

Output

in the first
in the second
in the third