@specialblend/unpromisify/dist/index.umd.js

convert async functions into callback style functions

(function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory(require('assert')) :
    typeof define === 'function' && define.amd ? define(['assert'], factory) :
    (global = global || self, global.index = factory(global.assert));
}(this, function (assert) { 'use strict';

    assert = assert && assert.hasOwnProperty('default') ? assert['default'] : assert;

    function unpromisify(handler) {
        return (...args) => {
            assert(args.length, 'unpromisified handler needs at least 1 argument');
            const params = args;
            const callback = args.pop();
            assert(typeof callback === 'function', 'provided callback argument must be a function');
            handler(...params)
                .then(data => callback(null, data))
                .catch(callback);
        };
    }

    return unpromisify;

}));