Array.prototype.asyncMap

asyncMap.js

Array.prototype.asyncMap = function (fn, callback) {
    var that = this, i, count = 0, errors = [], map = [];
    for (i = 0; i < this.length; i += 1) {
        (function iter(i) {
            fn(that[i], function (err, value) {
                err && errors.push(err);
                map[i] = value;
                count += 1;
                if (count === that.length) {
                    callback(errors.length ? errors : false, map);
                }
            });
        }(i));
    }
}

var redis = require('redis'),
    client = redis.createClient(),
    keys = ['hello', 'world'];

keys.asyncMap(function (value, callback) {
    client.get(value, callback);
}, function (err, values) {
    console.log(err || values);
    client.end();
});