Q.defer()和Promise()之间的区别

Question

我试图理解为什么以下代码与Q.defer()和Promise()的行为不同

案例1:当我使用Q.defer()时

getDocument(id)
.then(function (response) {
   console.log('in first then')
   return 'from two';
}).then(function (response) {
   console.log(response)
});

var getDocument=function(){
  var b = Q.defer();
    b.resolve('from getDocument'); // here will do some async operation..this is just an example
  return b.promise;
}

输出:

in first then
undefined

案例2:使用Promise()

getDocument(id)
.then(function (response) {
   console.log('in first then')
   return 'from two';
}).then(function (response) {
   console.log(response)
});

var getDocument=function(){
  return Promise.resolve('from getDocument');
}

输出:

in first then        
from two

题

1. 为什么输出会有差异？
2. 我知道Q.defer是一个反模式,但那么如何选择何时使用什么？

Answer 1

事实上，两个示例都返回相同的结果（相同的顺序）。检查这个 codepen示例

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var getDocument=function(){\n  var b = Q.defer();\n    b.resolve(\'Q from getDocument\'); // here will do some async operation..this is just an example\n  return b.promise;\n}\n\ngetDocument(1)\n.then(function (response) {\n   console.log(\'Q in first then\')\n   return \'Q from two\';\n}).then(function (response) {\n   console.log(response)\n});\n\nvar getDocumentP=function(){\n  return Promise.resolve(\'P from getDocument\');\n}\n\ngetDocumentP(1)\n.then(function (response) {\n   console.log(\'P in first then\')\n   return \'P from two\';\n}).then(function (response) {\n   console.log(response)\n});\n

\n\n

2) 你可以在这里看到 Q.defer 的一些用法：Q.defer you\xc2\xb4re 做错了

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