breakify

The opposite of promisify.

Seems silly, right? Except if you're in the middle of converting a project from callbacks to promises and you don't want to try to convert a few hundred files at once, some functions will still have to return their values through callbacks despite it being promises from there on down.

Usage

const breakify  = require('breakify');

function callbackFunction(callback) {
    const wrapper = async () => {
        const someFunctionAsync = promisify(someFunction);
        const value = await someFunctionAsync();

        if (value === 0) {
            throw new Error("You can't have 0, don't you know that?");
        }

        return value;
    }

    breakify(wrapper(), callback);
}

If your promiseReturningFunction returns a value, callback is called as callback(null, value), and if it throws an error, it is called as callback(err).