Nest one asynchronous function in another. Both functions are optional. MIT licence.

nest.js

function nest(before, after) {
    'use strict';

    if (typeof before !== 'function') {
        // Only after is defined, so just return it.
        if (typeof after === 'function') {
            return after;
        }

        // Neither function is defined, so return a function that just executes a callback.
        return function (callback) {
            callback();
        };
    }

    // before exists, so execute it first.
    return function (callback) {
        before(function (err) {
            if (err) {
                return callback(err);
            }

            // If newFunc is defined, execute it after before.
            if (typeof after === 'function') {
                return after(callback);
            }

            // If newFunc is not defined, just execute the callback after before.
            callback();
        });
    };
}