---
title: Check object equality
type: snippet
language: javascript
tags: [object,array,type,recursion]
cover: dying-flowers
dateModified: 2021-10-13T19:29:39+02:00
---

Performs a deep comparison between two values to determine if they are equivalent.

- Check if the two values are identical.
- Check if both values are `Date` objects with the same time, using `Date.prototype.getTime()`.
- Check if both values are non-object values with an equivalent value (strict comparison).
- Check if only one value is `null` or `undefined` or if their prototypes differ.
- If none of the above conditions are met, use `Object.keys()` to check if both values have the same number of keys.
- Use `Array.prototype.every()` to check if every key in `a` exists in `b` and if they are equivalent by calling `equals()` recursively.

```js
const equals = (a, b) => {
  if (a === b) return true;

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

  if (!a || !b || (typeof a !== 'object' && typeof b !== 'object'))
    return a === b;

  if (a.prototype !== b.prototype) return false;

  const keys = Object.keys(a);
  if (keys.length !== Object.keys(b).length) return false;

  return keys.every(k => equals(a[k], b[k]));
};
```

```js
equals(
  { a: [2, { e: 3 }], b: [4], c: 'foo' },
  { a: [2, { e: 3 }], b: [4], c: 'foo' }
); // true
equals([1, 2, 3], { 0: 1, 1: 2, 2: 3 }); // true
```