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Deep freeze object

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() 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

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