Check if two values are deeply equal

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Two objects with the same contents are not equal with the === operator, which compares references. To compare by value, use a deep equality check. This example shows the two built-in options.

Reference comparison fails even when the contents match.

const first = { a: 1 };
const second = { a: 1 };
console.log(first === second); // false

The standard library exports equal, a non-throwing deep comparison.

import { equal } from "jsr:@std/assert";

console.log(equal({ a: [1, 2] }, { a: [1, 2] })); // true
console.log(equal(new Map([["a", 1]]), new Map([["a", 1]]))); // true
console.log(equal({ a: 1 }, { a: 1, b: undefined })); // false

Node.js compatibility offers isDeepStrictEqual with the same job.

import { isDeepStrictEqual } from "node:util";

console.log(isDeepStrictEqual({ a: [1, 2] }, { a: [1, 2] })); // true

Strict means types matter. A string is never equal to a number.

console.log(isDeepStrictEqual({ a: 1 }, { a: "1" })); // false

In tests, prefer an asserting variant, which throws with a readable diff of the two values on failure.

import { assertEquals } from "jsr:@std/assert";

assertEquals({ a: [1, 2] }, { a: [1, 2] });
console.log("assertEquals passed"); // assertEquals passed

The Node.js equivalent assertion also works in Deno.

import { deepStrictEqual } from "node:assert/strict";

deepStrictEqual({ a: [1, 2] }, { a: [1, 2] });
console.log("deepStrictEqual passed"); // deepStrictEqual passed

Run this example locally using the Deno CLI:

deno run https://docs.deno.com/examples/scripts/deep_equal.ts

Check if two values are deeply equal

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