function flatten(arr) {
     // I'm a steamroller, baby
     arr.reduce(function (flat, toFlatten) {
        return flat.concat(Array.isArray(toFlatten) ? flatten(toFlatten) : toFlatten);
     },[]);
    }
    flatten([[['a']], [['b']]]);

assert.deepEqual(steamroller([[['a']], [['b']]]), ['a', 'b'], 'should flatten nested arrays');should flatten nested arrays: expected [ [ 'a' ], [ 'b' ] ] to deeply equal [ 'a', 'b' ]