Coding Challenge Practice - Question 106

The task is to implement deep equal _isEqual.

The boilerplate code

function isEqual(a, b) {
  // your code here
}

Handle primitive and reference equality

if (Object.is(a, b)) return true;

Reject non-objects early

if(typeof a !== "object" || typeof b !== 'object' || a === null || b === null) { 
return false; 
}

Track pairs already compared

const key = `${a}:${b}`;
if (seen.has(key)) {
  return true;
}
seen.set(key, true);

Compare time values. Two different Date values can be equal

if (a instanceof Date && b instanceof Date) {
  return a.getTime() === b.getTime();
}

Compare patterns and flags

if (a instanceof RegExp && b instanceof RegExp) {
  return a.toString() === b.toString();
}

Sort objects that represent different structures

if (Array.isArray(a) !== Array.isArray(b)) return false;

Objects with different numbers of properties cannot be equal

const keysA = Object.keys(a);
const keysB = Object.keys(b);

if (keysA.length !== keysB.length) {
  seen.delete(key);
  return false;
}

seen.delete(key) ensures cleanup on failure.

Each property in one object must be present in the other. Each value should be compared recursively

for (const key of keysA) {
  if (!keysB.includes(key)) {
    seen.delete(key);
    return false;
  }

  if (!isEqual(a[key], b[key], seen)) {
    seen.delete(key);
    return false;
  }
}

The final code

function isEqual(a, b, seen = new Map()) {
  // your code here
  if(Object.is(a,b)) return true;

  if(typeof a !== "object" || typeof b !== 'object' || a === null || b === null) {
    return false;
  }

  const key = `${a}:${b}`;
  if(seen.has(key)) {
    return true;
  }
  seen.set(key,true);

  if(a instanceof Date  && b instanceof Date) {
    return a.getTime() === b.getTime()
  }

  if(a instanceof RegExp && b instanceof RegExp) {
    return a.toString() === b.toString()
  }

  if(Array.isArray(a) !== Array.isArray(b)) return false;

  const keysA = Object.keys(a);
  const keysB = Object.keys(b);

  if(keysA.length !== keysB.length) {
    seen.delete(key);
    return false;
  };

  for(const key of keysA) {
    if(!keysB.includes(key)){
      seen.delete(key);
      return false;
    };
    if(!isEqual(a[key], b[key], seen)) {
      seen.delete(key);
      return false;
    };
  }
  seen.delete(key);
  return true;
}

That's all folks!