Deep object clone without recursion with recursion objects check

fork-with-recursive-check.js

var fork = function (source, unsafe) {
  var
    objmap = unsafe ? null : new Map(),
    targetOut = {__proto__: source.__proto__},
    target,
    stack = {0: {source: source, target: targetOut}},
    sp = 0,
    ss = 1,
    keys, key, j, scope, tmp;
  while ((scope = stack[sp++])) {
    keys = Object.keys(scope.source);
    j = keys.length;
    while (j--) {
      source = scope.source[key = keys[j]];
      if (source !== null && source === Object(source)) {
        if (!unsafe && (tmp = objmap.get(source))) {
          scope.target[key] = tmp;
        } else {
          scope.target[key] = target = {__proto__: source.__proto__};
          stack[ss++] = {source: source, target: target};
          if (!unsafe) {
            objmap.set(source, target);
          }
        }
      } else {
        scope.target[key] = source;
      }
    }
    delete stack[sp - 1];
  }
  target = source = stack = keys = key = scope = null;
  return targetOut;
};