Excises of Eloquent JavaScript 4th edition. Chapter 04 Problem 04. https://eloquentjavascript.net/04_data.html#i_IJBU+aXOIC

Eloquent JavaScript 0404 Deep comparison.js

// Your code here.
const deepEqual = (a, b) => {
  if (typeof a != 'object' || typeof b != 'object') return a === b;
  if (a == null || b == null) return a === b;
  
  const aKeys = Object.keys(a);
  const bKeys = Object.keys(b);
  if (aKeys.length != bKeys.length) return false;
  
  for (let i = 0 ; i < aKeys.length; i++) {
    if (!deepEqual(a[aKeys[i]], b[aKeys[i]])) return false;
  }
  
  return true;
}

let obj = {here: {is: "an"}, object: 2};
console.log(deepEqual(obj, obj));
// → true
console.log(deepEqual(obj, {here: 1, object: 2}));
// → false
console.log(deepEqual(obj, {here: {is: "an"}, object: 2}));
// → true