a higher-order-function that almost maintains the function signature, but not quite.

HOF1.ts

type ITask<I: $ReadOnlyArray<mixed>, O> = {
    (...r: I): ?O,
    lastError?: Error
}

function task <I: $ReadOnlyArray<mixed>, O>(inner: (...r: I) => O): ITask<I, O> {
    const wrapped: any = function wrapped() {
        try {
            return (inner: any).apply(this, arguments)
        } catch (err) { 
            (wrapped:any).lastError = err
        }

    }

    wrapped.lastError = null
    return wrapped
}

const t = task((str: string) => str.length)
t('hello') // good
t(123) // error, good
t(true) // error, good
console.log(t.lastError) // good
console.log(t.haha) // error, good