Solving "ReferenceError: structuredClone is not defined" in Jest Tests

Current Status

structuredClone() was added in Node.js 17.0.0 (Sept 2021). If you're using older Node versions or Jest environments like jsdom, manual solutions are needed.

Problem Overview

When running Jest tests in Node.js/TypeScript environments, you might encounter:

ReferenceError: structuredClone is not defined

This occurs because:

1. structuredClone() is unavailable in Node.js versions below 17
2. jsdom (used by Jest for browser-like environments) lacks its implementation
3. Your production environment supports it, but testing environment doesn't

Recommended Solutions

1. Update Node.js Version (Ideal Solution)

Upgrade to Node.js v17+:

# Check current version
node --version

# Update using nvm (recommended)
nvm install 18
nvm use 18

# Or via package manager (e.g., macOS Homebrew)
brew update && brew upgrade node

Verify support:

console.log('Native structuredClone support:', typeof structuredClone !== 'undefined');

Minimum Version Note

Ensure all team members and CI/CD pipelines update simultaneously to prevent environment inconsistencies.

2. Global Polyfill in Jest Configuration

For older Node versions or jsdom environments:

module.exports = {
  setupFiles: ['<rootDir>/jest.setup.ts'],
  // Other configurations...
};

declare global {
  function structuredClone<T>(obj: T): T;
}

// Add polyfill implementation
global.structuredClone = <T>(obj: T): T => {
  if (typeof globalThis.structuredClone === 'function') {
    return globalThis.structuredClone(obj);
  }
  return JSON.parse(JSON.stringify(obj)) as T;
};

3. Robust Polyfill Library

For complete feature support (Dates, Maps, custom classes, circular refs):

npm install @ungap/structured-clone
npm install -D @types/ungap__structured-clone

import structuredClone from '@ungap/structured-clone';

export const deepClone = <T>(obj: T): T => structuredClone(obj);

import { deepClone } from './utils/clone';

test('cloning test', () => {
  const original = new Map([['key', { value: 123 }]]);
  const cloned = deepClone(original);
  // Assertions...
});

Polyfill Limitations

While libraries provide better coverage, they can't perfectly replicate native browser behavior. Profile performance for large objects.

Environment-Specific Fixes

Fixing jsdom Environments

When using jest-environment-jsdom, add this to your setup file:

// Only define if missing in jsdom
if (!global.structuredClone) {
  global.structuredClone = function (obj) {
    return new Promise((resolve) => {
      const { port1, port2 } = new MessageChannel();
      port2.onmessage = (ev) => resolve(ev.data);
      port1.postMessage(obj);
    });
  };
}

Jest Version Conflicts

If you've updated Node but still see errors:

1. Upgrade Jest and related tools:

npm install --save-dev jest@29 ts-jest@29

2. Verify actual Node version in tests:

test('debug env', () => {
  console.log(`Test Node version: ${process.version}`);
});

Alternative: Switch to Vitest

For modern projects, consider Vitest (Jest-compatible API):

bash

npm remove jest ts-jest @types/jest
npm install -D vitest happy-dom @vitest/coverage-v8

js

import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    environment: 'happy-dom',
    setupFiles: './vitest.setup.ts',
    coverage: { provider: 'v8' },
  },
});

ts

import { expect, test } from 'vitest';

test('structuredClone works', () => {
  const original = { date: new Date() };
  const cloned = structuredClone(original);
  expect(cloned.date instanceof Date).toBe(true);
});

When to Use Which Solution?

Solution	Best For	Node Version Required	Complexity
Update Node.js	Greenfield projects, team alignment	v17+	★☆☆☆☆
Global Polyfill	Legacy projects, quick fixes	Any	★★☆☆☆
Polyfill Library	Complex objects, circular references	Any	★★★☆☆
Switch to Vitest	Performance-critical tests, modern stacks	v14+	★★★★☆

Historical Context

• structuredClone() entered browser specs in 2021 (MDN Docs)
• Node.js implemented it in v17.0.0 (September 2021)
• jsdom support is still pending as of 2024 (GitHub Issue)

Always prioritize upgrading Node.js where possible. For constrained environments, choose polyfills based on your data complexity and testing needs. Remember to document your solution for team awareness!