如何处理返回Promise的函数

Question

I'm wanting to declare a Promise's resolved value from a library like so.

// lib.js
exports.foo = function(){
    return new Promise(..)
}

// main.js
import { foo } from "./lib"

let x = await foo()

The await isn't working, and it seems everything I've tried leads to this error: UnhandledPromiseRejectionWarning: Unhandled promise rejection

Answer 1

See below, as CertainPerformance mentioned in the comments, you can't use await at the top level yet. Additionally, in order to use await you must add the async keyword to the function in which you await the resolution of a Promise .

// lib.js
exports.foo = function() {
    return new Promise(..)
};

// main.js
import { foo } from "./lib";

function async main() {
    let x = await foo();
};

Answer 2

You simply give the promise constructor a function(resolve,reject){ /* your code here with resolve(value); and reject(error);*/ } function(resolve,reject){ /* your code here with resolve(value); and reject(error);*/ } as a parameter then to call it and give the value to x you call var x; foo().then(function(value){ x=value; } ); //here you can optionally add .catch(function(error){ your error catch imp here}); if you want to catch your error var x; foo().then(function(value){ x=value; } ); //here you can optionally add .catch(function(error){ your error catch imp here}); if you want to catch your error