Convert a tree-like array into a flat array where the nested values are all part of the top-most array.

unnestArray.js

function unnestArray(arr, callback) {
  function recurse(arr, path) {
    function f(arr, opt_insertBefore) {
      dontAddRet = dontAddRet || !arguments.length;
      if (arr) {
        results.push.apply(opt_insertBefore ? results : after, recurse(arr, curPath));
      }
    }
    for (var ret, dontAddRet, curPath, results = [], after = [], i = 0, l = arr.length; i < l; i++) {
      dontAddRet = 0;
      ret = callback(arr[i], f, curPath = path.concat([i]), arr);
      results = results.concat(dontAddRet ? [] : [ret], after.splice(0));
    }
    return results;
  }
  return recurse(arr, []);
}