How to know if a function is async?

Question

I have to pass a function to another function, and execute it as a callback. The problem is that sometimes this function is async, like:

async function() {
          


        

Answer 1

Both @rnd, and @estus are correct.

But to answer the question with an actual working solution here you go

function isAsync (func) {
    const string = func.toString().trim();

    return !!(
        // native
        string.match(/^async /) ||
        // babel (this may change, but hey...)
        string.match(/return _ref[^\.]*\.apply/)
        // insert your other dirty transpiler check

        // there are other more complex situations that maybe require you to check the return line for a *promise*
    );
}

This is a very valid question, and I'm upset that someone down voted him. The main usecase for this type of checking is for a library/framework/decorators.

These are early days, and we shouldn't downvote VALID questions.