Promise.all中的Javascript array.push返回未定义

Question

我有一个承诺，我正在向Promise.all推送一个值，但它返回的是不确定的。

这是代码：

 var arr = []; var mypromise = new Promise((resolve, reject) => { resolve('mypromise'); arr.push(mypromise); }); Promise.all([arr]).then(values => { console.log(values); }); 

我怎样才能解决这个问题？

Answer 1

 var arr = []; var mypromise = new Promise((resolve, reject) => { resolve('mypromise'); }); arr.push(mypromise); Promise.all(arr).then(values => { console.log(values); }); 

尝试这个。

您的Promises实现不正确，请参阅此https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise

另外，您正在犯语法错误，例如arr.push应该在

 var mypromise = new Promise((resolve, reject) => { resolve('mypromise'); }); 

Promise.all接受一个数组，而您正在做的就是用另一个数组包装一个数组。

Answer 2

var arr = [];

var mypromise = new Promise((resolve, reject) => {
    resolve('mypromise');
    arr.push(mypromise);
}); 

Promise.all([arr]).then(values => {
    console.log(values);
});

我会向您指出您在代码中犯的一个错误...

var arr = []; // arr is currently an empty array
// when you create a variable mypromose, it is also currently undefined
var mypromise = new Promise((resolve, reject) => {
    resolve('mypromise');
    // even till now mypromise is undefined
    // what you are doing is arr.push(undefined)
    arr.push(mypromise);
}); 
// after it is completed, mypromise is now defined...

因此， arr = [undefined]