deepEqual

Recursively compares two values for structural equality. Handles primitives, plain objects, class instances (same prototype), arrays, Date, RegExp, Map, Set, ArrayBuffer, and typed arrays. Circular references are tracked with a WeakMap pair-cache; on cycle, the pair is assumed equal. Functions, Error instances, and other unsupported objects fall back to reference equality.

Try it

Import

import { deepEqual } from "1o1-utils";

import { deepEqual } from "1o1-utils/deep-equal";

Signature

function deepEqual({ a, b }: DeepEqualParams): boolean

Parameters

Name	Type	Required	Description
a	unknown	Yes	The first value to compare
b	unknown	Yes	The second value to compare

Returns

boolean — true if the values are deeply equal, false otherwise.

Examples

deepEqual({ a: { x: { n: 1 } }, b: { x: { n: 1 } } });
// => true

deepEqual({ a: [1, [2, 3]], b: [1, [2, 3]] });
// => true

deepEqual({ a: new Date("2024-01-01"), b: new Date("2024-01-01") });
// => true

deepEqual({ a: new Map([["x", 1]]), b: new Map([["x", 1]]) });
// => true

deepEqual({ a: { x: 1 }, b: { x: 2 } });
// => false

// React: skip a render only when the entire props tree is unchanged
function arePropsEqual(prev, next) {
  return deepEqual({ a: prev, b: next });
}

Edge Cases

• Uses Object.is, so NaN equals NaN and +0 is distinct from -0.
• Returns true for identical references (fast path).
• Same-prototype check runs first — a plain object never equals a class instance with identical fields.
• Symbol-keyed and non-enumerable properties are ignored.
• Date, RegExp, ArrayBuffer, and typed arrays compare structurally; Error instances fall back to reference equality.
• Map and Set deep comparisons use a greedy O(n²) match for elements not found by reference — fine for typical sizes, slow for very large collections.
• Circular references are detected with a WeakMap pair-cache; on cycle the pair is assumed equal.

Also known as

deep compare, structural equality, recursive equal, isEqual, value equality

Prompt suggestion

I'm using 1o1-utils (npm: https://www.npmjs.com/package/1o1-utils, GitHub: https://github.com/pedrotroccoli/1o1-utils, LLM context: https://pedrotroccoli.github.io/1o1-utils/llms.txt). Show me how to use deepEqual to compare two nested config objects for full structural equality