Implement deepEqual(a, b) handling NaN, -0, Dates, RegExp & circular refs

Question

Accepted Answer

**Approach:** Fast paths for SameValue (Object.is distinguishes -0/NaN), then type checks, then structural recursion with WeakMap for circular tracking.

```javascript
function deepEqual(a, b, seen = new WeakMap()) {
  if (Object.is(a, b)) return true;
  if (a == null || b == null || typeof a !== 'object' || typeof b !== 'object') return false;
  if (seen.has(a)) return seen.get(a) === b;
  seen.set(a, b);
  const protoA = Object.getPrototypeOf(a), protoB = Object.getPrototypeOf(b);
  if (protoA !== protoB) return false;
  if (a instanceof Date) return a.getTime() === b.getTime();
  if (a instanceof RegExp) return String(a) === String(b);
  if (a instanceof Map) {
    if (a.size !== b.size) return false;
    for (const [k,v] of a) if (!b.has(k) || !deepEqual(v, b.get(k), seen)) return false;
    return true;
  }
  if (a instanceof Set) {
    if (a.size !== b.size) return false;
    for (const v of a) if (!b.has(v)) return false;
    return true;
  }
  if (Array.isArray(a)) {
    if (a.

Implement deepEqual(a, b) handling NaN, -0, Dates, RegExp & circular refs

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Attempt it yourself

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Join the discussion

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