Resolving ReferenceError: TextEncoder is Not Defined in React Scripts Test Env JSDOM

When running tests in a React application using Jest with the JSDOM environment, you might encounter the error “ReferenceError: TextEncoder is not defined”. This issue typically arises because JSDOM, which simulates a browser environment for testing, does not include certain Node.js globals like TextEncoder by default. This can be particularly frustrating as it prevents tests from running successfully, especially when dealing with text encoding and decoding operations.

Understanding the Error

The error ReferenceError: TextEncoder is not defined occurs when running React scripts in a testing environment using jsdom. This error arises because the TextEncoder class, which is part of the Web API, is not available in the jsdom environment by default.

Detailed Explanation

1. What is TextEncoder?

   • TextEncoder is a built-in JavaScript class used to encode strings into UTF-8 byte streams. It’s part of the Web API and is typically available in browser environments.

2. Why the Error Occurs in jsdom:

   • jsdom Environment: jsdom is a JavaScript implementation of the DOM and HTML standards, primarily used for testing purposes. It simulates a browser environment but does not include all browser-specific APIs by default.
   • Node.js Environment: When running tests with jsdom, the environment is closer to Node.js than a real browser. Node.js does not include TextEncoder as a global object because it is not part of the Node.js standard library.
   • Missing Polyfills: Since TextEncoder is not available in Node.js, and jsdom does not provide it out of the box, any code relying on TextEncoder will throw a ReferenceError when executed in this environment.

How to Fix the Error

To resolve this error, you can manually add TextEncoder to the global scope in your test setup. Here are a few methods:

1. Using util Module in Node.js:

   // jest.setup.js
   global.TextEncoder = require('util').TextEncoder;
   global.TextDecoder = require('util').TextDecoder;
   

2. Custom Jest Environment:

   // custom-test-env.js
   const Environment = require('jest-environment-jsdom');
   
   module.exports = class CustomTestEnvironment extends Environment {
     async setup() {
       await super.setup();
       if (typeof this.global.TextEncoder === 'undefined') {
         const { TextEncoder, TextDecoder } = require('util');
         this.global.TextEncoder = TextEncoder;
         this.global.TextDecoder = TextDecoder;
       }
     }
   };
   

3. Using Polyfills:

   • You can also use polyfills like fast-text-encoding to add support for TextEncoder and TextDecoder in environments where they are not available.

By implementing one of these solutions, you can ensure that TextEncoder is defined in your testing environment, preventing the ReferenceError from occurring.

Common Causes

Here are the common causes of the ReferenceError: TextEncoder is not defined error when running React scripts in a JSDOM test environment:

1. Missing Polyfills:

   • Description: JSDOM does not natively include TextEncoder and TextDecoder.
   • Scenario: You need to manually add polyfills for these classes.
   • Solution: Use a polyfill like fast-text-encoding or add the following to your Jest setup file:

     global.TextEncoder = require('util').TextEncoder;
     global.TextDecoder = require('util').TextDecoder;
     

2. Outdated Dependencies:

   • Description: Older versions of JSDOM or Jest might not support TextEncoder and TextDecoder.
   • Scenario: Your project is using outdated versions of these libraries.
   • Solution: Update JSDOM and Jest to the latest versions.

3. Node.js Version:

   • Description: Certain Node.js versions do not include TextEncoder and TextDecoder as global objects.
   • Scenario: Your Node.js version is too old.
   • Solution: Upgrade to a newer version of Node.js that includes these classes globally.

4. Custom Test Environment:

   • Description: Jest might strip out some Node.js globals in its test environment.
   • Scenario: The default Jest environment does not include TextEncoder.
   • Solution: Create a custom Jest environment:

     const Environment = require('jest-environment-jsdom');
     module.exports = class CustomTestEnvironment extends Environment {
       async setup() {
         await super.setup();
         if (typeof this.global.TextEncoder === 'undefined') {
           const { TextEncoder, TextDecoder } = require('util');
           this.global.TextEncoder = TextEncoder;
           this.global.TextDecoder = TextDecoder;
         }
       }
     };
     

5. Incorrect Jest Configuration:

   • Description: Jest configuration might not be set up to include necessary setup files.
   • Scenario: Your Jest configuration is missing setup files that define TextEncoder.
   • Solution: Ensure your Jest configuration includes the setup file:

     {
       "jest": {
         "setupFilesAfterEnv": ["<rootDir>/jest.setup.js"]
       }
     }
     

These are the primary causes and solutions for the ReferenceError: TextEncoder is not defined error in a JSDOM test environment.

Solutions and Workarounds

To resolve the ReferenceError: TextEncoder is not defined error when running React scripts with Jest in a jsdom environment, follow these detailed steps:

Solution 1: Add Polyfills

1. Install the util package:

   npm install util
   

2. Create a Jest setup file (e.g., jest.setup.js):

   // jest.setup.js
   global.TextEncoder = require('util').TextEncoder;
   global.TextDecoder = require('util').TextDecoder;
   

3. Update your Jest configuration to include the setup file:

   // jest.config.js or package.json
   "jest": {
     "setupFilesAfterEnv": ["<rootDir>/jest.setup.js"]
   }
   

Solution 2: Custom Jest Environment

1. Create a custom Jest environment file (e.g., custom-test-env.js):

   const Environment = require('jest-environment-jsdom');
   
   module.exports = class CustomTestEnvironment extends Environment {
     async setup() {
       await super.setup();
       if (typeof this.global.TextEncoder === 'undefined') {
         const { TextEncoder, TextDecoder } = require('util');
         this.global.TextEncoder = TextEncoder;
         this.global.TextDecoder = TextDecoder;
       }
     }
   };
   

2. Update your Jest configuration to use the custom environment:

   // jest.config.js or package.json
   "jest": {
     "testEnvironment": "<rootDir>/custom-test-env.js"
   }
   

Solution 3: Use a Polyfill Library

1. Install a polyfill library like fast-text-encoding:

   npm install fast-text-encoding
   

2. Create a Jest setup file (e.g., jest.setup.js):

   // jest.setup.js
   const { TextEncoder, TextDecoder } = require('fast-text-encoding');
   global.TextEncoder = TextEncoder;
   global.TextDecoder = TextDecoder;
   

3. Update your Jest configuration to include the setup file:

   // jest.config.js or package.json
   "jest": {
     "setupFilesAfterEnv": ["<rootDir>/jest.setup.js"]
   }
   

These steps should help you resolve the TextEncoder is not defined error in your Jest tests. If you encounter any issues, feel free to ask for further assistance!

Best Practices

To avoid encountering the ‘ReferenceError: TextEncoder is not defined’ error in future projects, follow these best practices:

1. Polyfill TextEncoder and TextDecoder:

   • Add the following to your Jest setup file to ensure these classes are available globally:

     import { TextEncoder, TextDecoder } from 'util';
     global.TextEncoder = TextEncoder;
     global.TextDecoder = TextDecoder;
     

2. Use a Polyfill Library:

   • Consider using a polyfill library like fast-text-encoding to ensure compatibility:

     import 'fast-text-encoding';
     

3. Update Jest Configuration:

   • Ensure your Jest configuration includes the necessary setup files:

     "jest": {
       "setupFilesAfterEnv": ["<rootDir>/jest.setup.js"]
     }
     

4. Keep Dependencies Up to Date:

   • Regularly update Node.js, Jest, and other dependencies to their latest versions to avoid compatibility issues.

Keeping dependencies up to date is crucial as it ensures you have the latest features, security patches, and bug fixes, reducing the likelihood of encountering such errors.

To Resolve the ‘ReferenceError: TextEncoder is not defined’ Error in Jest Tests

Follow these steps:

1. Install fast-text-encoding: Run npm install fast-text-encoding to ensure compatibility with older browsers.
2. Create a Jest setup file: Add the following code to your jest.setup.js file to make TextEncoder and TextDecoder available globally:

const { TextEncoder, TextDecoder } = require('fast-text-encoding'); global.TextEncoder = TextEncoder; global.TextDecoder = TextDecoder;

3. Update Jest configuration: Include the setup file in your Jest configuration by adding "setupFilesAfterEnv": ["/jest.setup.js"] to your jest.config.js or package.json.

To avoid encountering this error in future projects, follow these best practices:

1. Polyfill TextEncoder and TextDecoder: Add the following code to your Jest setup file to ensure these classes are available globally:

import { TextEncoder, TextDecoder } from 'util'; global.TextEncoder = TextEncoder; global.TextDecoder = TextDecoder;

2. Use a Polyfill Library: Consider using a polyfill library like fast-text-encoding to ensure compatibility.
3. Update Jest Configuration: Ensure your Jest configuration includes the necessary setup files.
4. Keep Dependencies Up to Date: Regularly update Node.js, Jest, and other dependencies to their latest versions to avoid compatibility issues.

Understanding and resolving this error is crucial for smooth testing in React projects.