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ESLint vs Jest: What are the differences?
Key Differences between ESLint and Jest
ESLint and Jest are both popular tools used in web development. While they serve different purposes, they have key differences that set them apart from each other.
Purpose: ESLint is a static code analysis tool used to identify and report patterns and problems in JavaScript code. It helps enforce coding standards and best practices. On the other hand, Jest is a testing framework primarily used for testing JavaScript code. It provides a testing environment and tools for writing unit tests, integration tests, and snapshots.
Configuration: ESLint requires a configuration file (
.eslintrc) to set rules, environments, and extensions for linting. It offers a wide range of configurable options to customize the linting process. In contrast, Jest requires a configuration file (jest.config.js) to define its behavior and settings for running tests. It provides options to configure test environments, test patterns, and reporter output.Usage: ESLint can be integrated into various development environments, editors, and build systems. It helps developers catch syntax errors, logical errors, and maintain consistent code style. It can be run as part of a build process or in an integrated development environment (IDE). Jest, on the other hand, is primarily used in the command line interface (CLI) to run tests. It provides a rich set of matchers, assertions, and utilities for testing JavaScript code.
Test Coverage: Jest includes built-in functionality for generating code coverage reports. It can track the lines of code executed during the tests and provide insights into the code coverage percentage. ESLint, however, does not have built-in support for code coverage analysis. Developers would need to use separate tools or plugins to analyze test coverage when using ESLint.
Test Runners: Jest comes with its own test runner, which allows parallel and isolated execution of test cases. It has built-in features like test filtering, test watch mode, and test caching for faster execution. ESLint, on the other hand, is not a test runner and does not have the ability to execute tests. It focuses on analyzing code and providing feedback on potential issues.
Integration with Other Tools: Both ESLint and Jest can be integrated with various other tools and libraries. ESLint has integrations with editors like Visual Studio Code and build systems like Webpack. It can also be extended with plugins to support additional rules and custom configurations. Jest, on the other hand, can be integrated with tools like Babel for transpiling code, Enzyme for testing React components, and Puppeteer for testing web applications.
In summary, ESLint is a code analysis tool used to enforce coding standards and catch potential issues in JavaScript code, while Jest is a testing framework used for writing and running tests. They differ in their purpose, configuration, usage, test coverage, test runners, and integration capabilities.
Scenario: I want to integrate Prettier in our code base which is currently using ESLint (for .js and .scss both). The project is using gulp.
It doesn't feel quite right to me to use ESLint, I wonder if it would be better to use Stylelint or Sass Lint instead.
I completed integrating ESLint + Prettier, Planning to do the same with [ Stylelint || Sasslint || EsLint] + Prettier.
And have gulp 'fix' on file save (Watcher).
Any recommendation is appreciated.
In the case of .js files I would recommend using both Eslint and Prettier.
You can set up Prettier as an Eslint rule using the following plugin:
https://github.com/prettier/eslint-plugin-prettier
And in order to avoid conflicts between Prettier and Eslint, you can use this config:
https://github.com/prettier/eslint-config-prettier
Which turns off all Eslint rules that are unnecessary or might conflict with Prettier.
you don't actually have to choose between these tools as they have vastly different purposes. i think its more a matter of understanding how to use them.
while eslint and stylelint are used to notify you about code quality issues, to guide you to write better code, prettier automatically handles code formatting (without notifying me). nothing else.
prettier and eslint both officially discourage using the eslint-plugin-prettier way, as these tools actually do very different things. autofixing with linters on watch isnt a great idea either. auto-fixing should only be done intentionally. you're not alone though, as a lot of devs set this up wrong.
i encourage you to think about what problem you're trying to solve and configure accordingly.
for my teams i set it up like this: - eslint, stylelint, prettier locally installed for cli use and ide support - eslint config prettier (code formatting rules are not eslints business, so dont warn me about it) - vscode workspace config: format on save - separate npm scripts for linting, and formatting - precommit hooks (husky)
so you can easily integrate with gulp. its just js after all ;)
Pura vida! Well, I had a similar issue and at the end I decided to use Stylelint + Prettier for that job, in our case, we wanted that our linting process includes the SCSS files and not only the JS file, base on that we concluded that using only ESLint to do both things wasn't the best option, so, we integrated prettier with Stylelint, and for that we used a neat plugin that allowed us to use Prettier inside Stylelint here is the link, https://github.com/prettier/stylelint-prettier#recommended-configuration, I hope that this can help you, hasta pronto!, :)
As we all know testing is an important part of any application. To assist with our testing we are going to use both Cypress and Jest. We feel these tools complement each other and will help us get good coverage of our code. We will use Cypress for our end to end testing as we've found it quite user friendly. Jest will be used for our unit tests because we've seen how many larger companies use it with great success.
Postman will be used to do integration testing with the backend API we create. It offers a clean interface to create many requests, and you can even organize these requests into collections. It helps to test the backend API first to make sure it's working before using it in the front-end. Jest can also be used for testing and is already embedded into React. Not only does it offer unit testing support in javascript, it can also do snapshot testing for the front-end to make sure components are rendering correctly. Enzyme is complementary to Jest and offers more functions such as shallow rendering. UnitTest will be used for Python testing as it is simple, has a lot of functionality and already built in with python. Sentry will be used for keeping track of errors as it is also easily integratable with Heroku because they offer it as an add-on. LogDNA will be used for tracking logs which are not errors and is also a Heroku add-on. Its good to have a separate service to record logs, monitor, track and even fix errors in real-time so our application can run more smoothly.
Pros of ESLint
- Consistent javascript - opinions don't matter anymore8
- Free6
- IDE Integration6
- Customizable4
- Focuses code review on quality not style2
- Broad ecosystem of support & users2
Pros of Jest
- Open source36
- Mock by default makes testing much simpler32
- Testing React Native Apps23
- Parallel test running20
- Fast16
- Bundled with JSDOM to enable DOM testing13
- Mock by default screws up your classes, breaking tests8
- Out of the box code coverage7
- Promise support7
- One stop shop for unit testing6
- Great documentation3
- Assert Library Included2
- Built in watch option with interactive filtering menu1
- Preset support1
- Can be used for BDD0
- Karma0
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Cons of ESLint
Cons of Jest
- Documentation4
- Ambiguous configuration4
- Difficult3
- Many bugs still not fixed months/years after reporting2
- Multiple error messages for same error2
- Difficult to run single test/describe/file2
- Ambiguous2
- Bugged2
- BeforeAll timing out makes all passing tests fail1
- Slow1
- Reporter is too general1
- Unstable1
- Bad docs1
- Still does't support .mjs files natively1
- Can't fail beforeAll to abort tests1
- Interaction with watch mode on terminal0
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