deepFreeze

Deep freezes an object.

• Use Object.keys() to get all the properties of the passed object, Array.prototype.forEach() to iterate over them.
• Call Object.freeze(obj) recursively on all properties, applying deepFreeze() as necessary.
• Finally, use Object.freeze() to freeze the given object.

const deepFreeze = obj => {
  Object.keys(obj).forEach(prop => {
    if (typeof obj[prop] === 'object') deepFreeze(obj[prop]);
  });
  return Object.freeze(obj);
};

'use strict';

const val = deepFreeze([1, [2, 3]]);

val[0] = 3; // not allowed
val[1][0] = 4; // not allowed as well