Promise.all（）基于返回Promises的函数

Question

I am trying to use Promise.all() with Promises encapsulated on functions:

function fn1(val){

    return new Promise((resolve, reject) => {  

       /* promise body */        
    });    
}


function fn2(val){

    return new Promise((resolve, reject) => {  

       /* promise body */        
    });    
}



fn1(data)
.then((val) => fn2(val))
.catch((error) => alert(error)



Promise.all([fn1, fn2]).then(() => alert("Done!"))

This seems not possible as the Promise.all([fn1, fn2]) executes directly instead of waiting for the promises to success.

I know I could just chain another .then() to the thenable structure, but I wonder if there is any way of using Promise.all() on a context where Promises are contained into functions.

Answer 1

Promise.all takes an Array of Promise s.

Since your functions return Promises you can call the functions while declaring the Promise.all Array and they will be replaced by the Promises.

 // error handling (reject/catch) omitted for brevity. function fn1 (val) { return new Promise(resolve => { resolve('foo ' + val) }) } function fn2 (val) { return new Promise(resolve => { resolve('bar ' + val) }) } Promise.all([fn1(1), fn2(2)]) .then(result => console.log(result))