Public
Edited
Jun 1, 2023
Paused
1 star
function IsPromise(x) {
const hasConstructor = Object.prototype.hasOwnProperty.call(x, 'constructor');
const savedConstructor = x.constructor;
x.constructor = undefined;
try {
Promise.prototype.then.call(x, () => {});
return true;
} catch(e) {
return false;
} finally {
if (hasConstructor) {
x.constructor = savedConstructor;
} else {
delete x.constructor;
}
}
}
IsPromise(Promise.resolve(42))
IsPromise(new Promise(resolve => resolve(42)))
{
class MyPromise extends Promise {
constructor(executor) {
super(executor);
}
}
return IsPromise(new MyPromise(resolve => resolve(42)));
}
function CanPassthroughPromiseResolve(x) {
if (IsPromise(x)) {
const xConstructor = x.constructor;
if (xConstructor === Promise) {
return true;
}
}
return false;
}
CanPassthroughPromiseResolve(Promise.resolve(42))
CanPassthroughPromiseResolve(new Promise(resolve => resolve(42)))
{
class MyPromise extends Promise {
constructor(executor) {
super(executor);
}
}
return CanPassthroughPromiseResolve(new MyPromise(resolve => resolve(42)));
}
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