角度承诺对象之间的差异

Question

What is the difference between promise 1 and promise 2? The 1st one has only $$state property, the second one has additionally error and success callback. Why are they different?

<div ng-app="app">
 <div ng-controller="TodoCtrl">

  </div>
 </div>




angular.module('app', [])
 .controller('TodoCtrl', function ($scope, $http) {
//promise 1    
console.log('p1',$http.get("/echo/json/").then(
  function(){ console.log('s1',arguments); }, 
  function(){ console.log('e1',arguments); }
 )
);

var p = $http.get("/echo/json/");
//promise 2
console.log('p2',p);
p.then(
  function(){ console.log('s2',arguments);}, 
  function(){console.log('e2',arguments);});
}
);

console log says:

p1 Promise { $$state: Object }
   $$state: Object
   __proto__: Object
 p2 Promise { $$state: Object } 
      $$state: Object
      error: (fn) 
      success: (fn)
      __proto__: Object

Answer 1

In your first case, you call $http.get("/echo/json/") that returns a Promise. After that you apply "then" method with callbacks to this promise (that returns you new promise), and after that your console output is executed (and you have this new promise there). Callback functions are executed when real result comes back. In the second case, you create promise, logs it (as a first created promise, nothing more, no callbacks), and after that you apply "then" method with callbacks to your promise. Again, callback functions will be executed after results are received. You can find description in Promise API documentation .