asyncMap.js

function asyncMap(inputs, func, callback) {
    var remaining = inputs.length,
        results = [],
        errors = [];

    inputs.forEach(function(d, i) {
        func(d, function done(err, data) {
            errors[i] = err;
            results[i] = data;
            remaining --;
            if (!remaining) callback(errors, results);
        });
    });
}