Question

我有一个承诺，我正在向Promise.all推送一个值，但是它返回的是未定义的。

代码如下：

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

我该如何解决？

Answer 1

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

试试这个。

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

此外，您正在犯语法错误，例如arr.push应该在

之后

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

Promise.all都接受一个数组，而您正在做的就是将一个数组包装到另一个数组中。

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]

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

2 个答案: