有没有办法自定义promise.all？

Question

As per the current behavior, The Promise.all() method returns a single Promise that resolves when all of the promises passed as an iterable have resolved or when the iterable contains no promises. It rejects with the reason for the first promise that rejects.

For example:

var promise1 = Promise.resolve(3);
var promise2 = 42;
var promise3 = new Promise(function(resolve, reject) {
  setTimeout(resolve, 100, 'foo');
});

Promise.all([promise1, promise2, promise3]).then(function(values) {
  console.log(values);
});
// expected output: Array [3, 42, "foo"]

Currently, I was trying to implement a polyfill something similar to promise.all (Like, promise.sequenceAll ) where the result of the 1st promise will be fed to the next promise.

var promise1 = Promise.resolve(3);
var promise2 = 42;
var promise3 = new Promise(function(resolve, reject) {
  setTimeout(resolve, 100, 'foo');
});

Promise.sequenceAll([promise1, promise2, promise3]).then(function(values) {
  console.log(values);
});

Expected output: The result of promise1 will be passed to the promise2 as an argument. If any of the promises rejects, then it will execute promise.catch();

Answer 1

You can just do this and return the resolved value of the first promise from a .then() handler which will make it become the resolved value of the resulting promise:

Promise.all([promise1, promise2, promise3]).then(([v1]) => {
   // make the resolved value of the first promise be the resolved value
   // of the subsequent promise
   return v1;
}).then((value) => {
   // v1 is now the resolved value of the chain
   console.log(value);
});

You could encapsulate that behavior in your own function is you wanted, though it's pretty easy to just add a .then() handler onto an existing Promise.all() when you want this behavior.

Answer 2

Seems that promise.pipe is exactly what you need

https://www.npmjs.com/package/promise.pip

Sadly, I don't have an ability to check right now but it seems possible using Array.reduce(), take a look at this article: https://css-tricks.com/why-using-reduce-to-sequentially-resolve-promises-works/ They were able to at least sequentially execute them.