为什么直接将Promise.all传递给.then函数会抛出错误？

Question

I want to pass directly Promise.all to a .then function like:

const test = [
    Promise.resolve(),
    Promise.resolve(),
    Promise.resolve(),
    Promise.resolve()
];

Promise.resolve(test) // It's supposed to be an AJAX call
.then(Promise.all) // Get an array of promises
.then(console.log('End');

But this code throws an error Uncaught (in promise) TypeError: Promise.all called on non-object .

When I remove the shorthand syntax, it works:

Promise.resolve(test)
.then(queries => Promise.all(queries))
.then(console.log('End'));

So why a Promise.all passed directly to a .then throws an error ? (And why a console.log works fine ?)

Answer 1

You need to bind Promise.all.bind(Promise)

From ES2015 spec :

The all function requires its this value to be a constructor function that supports the parameter conventions of the Promise constructor.

Or better use it directly on array.

 const test = [ Promise.resolve(1), Promise.resolve(2), Promise.resolve(3), Promise.resolve(4) ] Promise.resolve(test) .then(Promise.all.bind(Promise)) .then(x => console.log(x)) Promise.all(test) .then(x => console.log(x))