assert

Last updated Apr 23, 2026 Note

For compatibility dates of 2026-08-04 or later, Workers enables both nodejs_compat and nodejs_compat_v2 by default. These flags are not used for these compatibility dates. Existing projects do not need to remove them when updating their compatibility date. For earlier dates, add nodejs_compat to your Wrangler configuration file to opt in. For instructions to turn off Node.js compatibility, refer to the Node.js compatibility flag.

The node:assert ↗︎ module in Node.js provides a number of useful assertions that are useful when building tests.

import { strictEqual, deepStrictEqual, ok, doesNotReject } from "node:assert";

strictEqual(1, 1); // ok!
strictEqual(1, "1"); // fails! throws AssertionError

deepStrictEqual({ a: { b: 1 } }, { a: { b: 1 } }); // ok!
deepStrictEqual({ a: { b: 1 } }, { a: { b: 2 } }); // fails! throws AssertionError

ok(true); // ok!
ok(false); // fails! throws AssertionError

await doesNotReject(async () => {}); // ok!
await doesNotReject(async () => {
    throw new Error("boom");
}); // fails! throws AssertionError

Note

In the Workers implementation of assert, all assertions run in, what Node.js calls, the strict assertion mode. In strict assertion mode, non-strict methods behave like their corresponding strict methods. For example, deepEqual() will behave like deepStrictEqual().

Refer to the Node.js documentation for assert ↗︎ for more information.

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