flatten.js

var push = [].push;

var flatten = function(array) {
    return [].concat(array).reduce(function(ret, curr) {
        if (~['Array', 'Arguments'].indexOf(
            Object.prototype.toString
            .call(curr)
            .slice('[object '.length, -1)
        )) {
            push.apply(ret, flatten([].slice.call(curr)))
        } else {
            ret.push(curr);
        }
        return ret;
    }, []);
}