mrtcode

var a = [[1,2,[3]],4];

function flat(a) {

  function _flat(a, depth) {
    var b = [];

    if(depth>100) throw 'too deep';

    for(var i=0;i<a.length;i++) {

mrtcode

var locks = {};

function lock(id, callback) {
    var lock = locks[id];

    if (lock) {
        lock.push(callback);
    } else {
        locks[id] = [];
        callback(unlock(id));