denoland/deno · error · TypeError

ERR_CONSTRUCT_CALL_REQUIRED

ERR_CONSTRUCT_CALL_REQUIRED

Error message

Class constructor Assert cannot be invoked without `new`

What it means

The assert strict-mode class in Deno's node:assert polyfill must be constructed with new (ext/node/polyfills/assert.ts:71): calling Assert() as a plain function throws ERR_CONSTRUCT_CALL_REQUIRED('Assert'). Instances carry assertion options ({ strict, skipPrototype, diff }) and expose the full assertion surface (ok, equal, rejects, etc.) on their prototype, mirroring Node's class-based assert API introduced for per-instance configuration.

Source

Thrown at ext/node/polyfills/assert.ts:71

  ObjectPrototypeIsPrototypeOf,
  ReflectApply,
  ReflectHas,
  RegExpPrototypeExec,
  SafeArrayIterator,
  StringPrototypeIndexOf,
  StringPrototypeSlice,
  StringPrototypeSplit,
  String,
  Symbol,
} = primordials;

const kOptions = Symbol("options");

const NO_EXCEPTION_SENTINEL = {};

function Assert(options) {
  if (!new.target) {
    throw new ERR_CONSTRUCT_CALL_REQUIRED("Assert");
  }

  options = ObjectAssign({
    __proto__: null,
    strict: true,
    skipPrototype: false,
  }, options);

  const allowedDiffs = ["simple", "full"];
  if (options.diff !== undefined) {
    validateOneOf(options.diff, "options.diff", allowedDiffs);
  }

  this.AssertionError = AssertionError;
  ObjectDefineProperty(this, kOptions, {
    __proto__: null,
    value: options,
    enumerable: false,

View on GitHub (pinned to 89f33cbef2)

Solutions

1. Always instantiate: const a = new Assert({ strict: true, diff: 'full' })
2. For plain strict assertions, just use the default export: const assert = require('assert').strict; assert(ok)
3. If you only need assert() itself, the top-level function never requires new

Example fix

// before
const a = require('assert').Assert();

// after
const a = new (require('assert').Assert)({ strict: true });

const assert = require('node:assert'); const a = new assert.Assert({ strict: true });

try { Assert(); } catch (e) { if (e.code === 'ERR_CONSTRUCT_CALL_REQUIRED') a = new Assert(); else throw e; }

When it happens

Trigger: const a = assert.strict; a(); is fine — the throw happens only for const A = assert.Assert; A(); without new, or subclass invocation via A.call(this) patterns; also Reflect.apply(Assert, undefined, []).

Common situations: Destructuring code like const { Assert } = require('assert') and calling it directly expecting a factory; bundlers or old transpilers that drop `new` from class calls; copy-pasted snippets targeting Node's older function-style API.

Related errors

• ERR_ASSERTION
• ERR_INVALID_ARG_VALUE
• ERR_INVALID_RETURN_VALUE
• ERR_INVALID_ARG_TYPE
• ERR_AMBIGUOUS_ARGUMENT

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/d2dbd14476eb2320. Report an issue: GitHub.