deep copy

deep.js

class Stack {
  constructor(initialCapacity) {
    initialCapacity = initialCapacity | 0;
    if (!(initialCapacity > 0)) {
      initialCapacity = 1;
    }

    this._arr = new Array(initialCapacity);
    this._n = 0;
  }

  push(el) {
    if (this._n >= this._arr.length) {
      this._arr.length *= 2;
    }
    this._arr[this._n] = el;
    ++this._n;
  }

  pop() {
    --this._n;
  }

  top() {
    return this._arr[this._n - 1];
  }

  empty() {
    return !(this._n > 0);
  }
}

class CopyTask {
  constructor(parent, parentKey, obj) {
    this.parent = parent;
    this.parentKey = parentKey;
    this.obj = obj;
  }
}

function skeletonClone(obj) {
  if (Array.isArray(obj)) {
    return new Array(obj.length);
  } else {
    return Object.create(Object.getPrototypeOf(obj));
  }
}

function deepClone(root) {
  var stack = new Stack();
  var container = {};
  stack.push(new CopyTask(container, 'copied', root));

  while (!stack.empty()) {
    var task = stack.top();
    stack.pop();

    var obj = task.obj;
    
    var copied = skeletonClone(obj);
    task.parent[task.parentKey] = copied;

    var keys = Object.keys(obj);
    for (var i = 0; i < keys.length; ++i) {
      var key = keys[i];
      var child = obj[key];

      if (child != null) {
        switch (typeof child) {
          case 'string':
          case 'number':
          case 'boolean':
          case 'symbol':
          case 'undefined':
            copied[key] = child;
            break;
          default:
            stack.push(new CopyTask(copied, key, obj[key]));
        }
      } else {
        copied[key] = null;
      }
    }
  }

  return container.copied;
}

var arr = ['c', 'd', 'e'];
arr.hello = 123;

var test = {
  'hello': {
    'a': 0,
    'b': {},
  },
  [1]: 'b',
  'world': arr,
};

var copied = deepClone(test);

console.log('original:', test);
console.log('copied:', copied);

arr[0] = 'I am changed';
console.log('\nMutating original\n')

console.log('original:', test);
console.log('copied:', copied);