Working with Assert Module
1. Using assert() for Truthy Checks
Example
import assert from "node:assert/strict";
assert(value, "value must be truthy");
Note: Always import assert/strict — uses === instead of ==.
2. Using assert.ok for Boolean Checks
| API | Equivalent |
|---|
assert.ok(x, msg) | Same as assert(x, msg) |
3. Using assert.strictEqual (===)
| Check | Behavior |
|---|
strictEqual(a,b) | Throws if a !== b |
| NaN handling | NaN === NaN in strict mode (Object.is) |
4. Using assert.notStrictEqual (!==)
| API | Throws When |
|---|
notStrictEqual(a,b) | a === b |
5. Using assert.deepStrictEqual
Example
assert.deepStrictEqual({ a: [1, 2] }, { a: [1, 2] }); // OK
assert.deepStrictEqual(new Map([["a",1]]), new Map([["a",1]]));
| Compares | Detail |
|---|
| Own enumerable props | Recursively |
| Prototypes | Must match |
| Symbols | Compared |
6. Using assert.notDeepStrictEqual
| API | Throws When |
|---|
notDeepStrictEqual(a,b) | Deep equal |
7. Using assert.throws (error testing)
Example
assert.throws(() => JSON.parse("nope"), {
name: "SyntaxError",
message: /Unexpected token/
});
8. Using assert.rejects
Example
await assert.rejects(fetchUser(-1), { message: /not found/ });
9. Using assert.doesNotThrow
| API | Use |
|---|
doesNotThrow(fn) | Asserts no synchronous throw |
doesNotReject(promise) | Async variant |
10. Using assert.ifError
| API | Behavior |
|---|
assert.ifError(err) | Throws if err is truthy |
| Use case | Node-style callbacks |
11. Using assert.match
| API | Use |
|---|
assert.match(str, /pattern/) | Throws if no match |
assert.doesNotMatch | Reverse |
12. Creating Custom Assertion Messages
Example: AssertionError
throw new assert.AssertionError({
message: "user must be active",
actual: user.status,
expected: "active",
operator: "==="
});