Function isPromise

isPromise<T>(v: T | Promise<T>): v is Promise<T>

Checks if value is Promise, acts as a typescript safeguard.

Narrows T | Promise<T> to Promise<T> cleanly in normal usage; works with Array.prototype.filter to extract promises from a mixed array.

Type Parameters

T

Parameters

v: T | Promise<T>

Returns v is Promise<T>

Example

isPromise(Promise.resolve(5))   // true
isPromise(5)                    // false

function check(v: Promise<number> | number) {
    if (isPromise(v)) {
        // v: Promise<number>
    }
}

const arr: (Promise<number> | number)[] = [...]
arr.filter(isPromise) // Promise<number>[]