javascript - 为什么 console.log() 在 Promises 的resolve() 函数中立即执行？

Question

以下面为例:

function sayHello () {
  return new Promise( function(resolve, reject) {
    console.log('Were inside the promise');

    return resolve(5);
  })
}

sayHello().then(function(success){
  console.log(success)
})

console.log('Im outside the promise')

我们知道它按以下顺序执行:

Were inside the promise
Im outside the promise
5

然后，对于类似的事情:

function sayHello () {
  return new Promise( function(resolve, reject) {
    console.log('Were inside the promise');

    return resolve((function(){
      return 5
    })());
  })
}

sayHello().then(function(success){
  console.log(success)
})

console.log('Im outside the promise')

它返回与前一个示例相同的 console.log 输出序列。太棒了，有道理；无论resolve中的值是什么，当then()执行时，都会作为参数通过管道传输。

为什么，当我有类似下面的内容时:

function sayHello () {
  return new Promise( function(resolve, reject) {
    console.log('Were inside the promise');

    return resolve(console.log(5));
  })
}

sayHello().then(function(success){
  console.log(success)
})

console.log('Im outside the promise')

我收到这个订单了吗:

Were inside the promise
5
Im outside the promise

Answer 1

当解析器函数在下一个“tick”中被调用时，它的参数会立即被评估。这就是为什么您会在第三个代码段示例中看到 console.log(5) 在 before then 回调执行。如果您将第二个代码片段更改为:

function sayHello() {
  return new Promise(function(resolve, reject) {
    console.log('Were inside the promise');
    return resolve((function() {
      console.log('Inside resolver argument');
      return 5
    })());
  })
}
sayHello().then(function(success) {
  console.log(success)
});
console.log('Im outside the promise');