Using ESLint and Prettier in a TypeScript Project

Robert Cooper on February 16, 2019

Originally posted on my blog. When it comes to linting TypeScript code, there are two major linting options to choose from: TSLint and ESLint.... [Read Full]
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I ran a problem today with this setup. If I run prettier --single-quote --write then eslint --fix, it will fail because of this line:

                    {state === PENDING
                        ? Array(10)
                              .fill(true)

prettier wants the above, but eslint wants:

                    {state === PENDING
                        ? Array(10)
                            .fill(true)

(so 28 spaces instead of 30).

Any tips? I am kinda stuck.

 

You need to run prettier through ESLint, otherwise you'll get these kind of conflicts.

 

It seems that vscode is running prettier when formatting on save, rather than eslint! I will look into it on Monday when I back with my laptop :P

You need to make sure to turn off the formatOnSave in VSCode for your JavaScript and Typescript files. Here are the settings:

"editor.formatOnSave": true,
"[javascript]": {
    "editor.formatOnSave": false,
  },
  "[javascriptreact]": {
    "editor.formatOnSave": false,
  },
  "[typescript]": {
    "editor.formatOnSave": false,
  },
  "[typescriptreact]": {
    "editor.formatOnSave": false,
  },

Then to make sure you get ESLint to fix problems on save, make sure you have the following settings in VS Code:

"eslint.autoFixOnSave": true,
  "eslint.validate": [
    "javascript",
    "javascriptreact",
    {"language": "typescript", "autoFix": true },
    {"language": "typescriptreact", "autoFix": true }
  ],

Thanks! But there is still an issue with it :( It seems like a conflict between eslint(prettier/prettier) and eslint(@typescript-eslint/indent). I also feel like eslint is running twice or something. For now I have set:

    rules: {
        '@typescript-eslint/indent': 'off',
    }

Here's my full eslint config file:

module.exports = {
    parser: '@typescript-eslint/parser',
    extends: [
        'plugin:@typescript-eslint/recommended',
        'plugin:prettier/recommended',
        'plugin:react/recommended',
    ],
    parserOptions: {
        ecmaVersion: 2018,
        sourceType: 'module',
        ecmaFeatures: {
            jsx: true,
        },
        project: './tsconfig.json',
        tsconfigRootDir: './',
    },
    settings: {
        react: {
            version: 'detect',
        },
    },
    rules: {
        '@typescript-eslint/interface-name-prefix': 'always',
        '@typescript-eslint/no-explicit-any': 'always',
        '@typescript-eslint/explicit-function-return-type': 'off',
        '@typescript-eslint/no-non-null-assertion': 'off',
        '@typescript-eslint/no-use-before-define': 'off',
        '@typescript-eslint/member-delimiter-style': {
            delimiter: 'none',
            requireLast: true,
        },
    }
}

VSCode User settings: hastebin.com/jucodoheqi.json
VSCode Workspace settings: hastebin.com/anenanupuh.json

I think your extends array should be the following (I've added comments explaining things):

    extends: [
        'plugin:@typescript-eslint/recommended', // uses typescript-specific linting rules
        'plugin:react/recommended', // uses react-specific linting rules
        'plugin:prettier/recommended', // enables eslint-plugin-prettier and eslint-config-prettier
        'prettier/react', // disables react-specific linting rules that conflict with prettier
    ],

Still didn't seem to fix the issue! Although I also ran into this last week, which I have not been able to solve. Something must be wrong with my setup somewhere haha. Check it out:

Prettier wants this:

export default function Heading(
    props: HTMLProps<HTMLHeadingElement> & {
        as?: AsTags
        withComponent?: HeadingTags
    },
) /* .... */

But typescript fails to compile because of the missing comma after as?: AsTags as it wants as?: AsTags, but prettier removes it ._.

Thanks for providing the snippets though. If you can shed any light on this one I would appreciate it a ton :3

 

Just curious about your opinion on if you need to use a linter to check code if you use typescript in strict mode. For styles, for sure using prettier makes sens to me.

 

Good question. Using a linter allows you to check on a lot of stuff that isn't covered by the TypeScript compiler. For example, if you take a look at some of these ESLint rules for TypeScript code, you'll find a lot of rules related to code style that can be enforced with a linter.

Here are a few examples:

  • @typescript-eslint/explicit-function-return-type: Require explicit return types on functions and class methods
  • @typescript-eslint/generic-type-naming: Enforces naming of generic type variables
  • @typescript-eslint/no-array-constructor: Disallow generic Array constructors
  • @typescript-eslint/no-unused-vars: Disallow unused variables
 

all of the rules above are again kinda of stylistic (last one is already covered directly by typescript). If something is wrong, typescript will tell u during compile regardless whether you specify function return type explicitly or not.. I also depend on computer types in typescript (maybe thats why i think like this for linter with strict mode)

Well if you don't mind having the code written in a project not conform to code style rules, then a linter is of no value. You just might have a large variance in the way code is structured/ordered, variables are named, and other code style related things.

When I'm working on a project, I prefer to look at the code base and have it look like it was all written by the same person. A linter helps achieve this in my opinion.

And there's still things like no explicit any that can be enforced by the linter.

 

Thanks for the great article. I was just busy on writing something similar on getting Gatsby set-up with TypeScript, ESLint, and Prettier. The set-up is pretty similar as well!

Never mind the question below, it's the eslint.validatesetting in VS code :D, I should've taken a note from your article ;).

Question for reference:

I wonder if you've encountered the same thing though: In VSCode, the editor doesn't seem to show me errors from my ESLint file with this setup, whether they're an extension of rules or added explicitly, just the TypeScript errors. Of course, when linting the errors _do show up. Any ideas on how to fix this?_

 

Just took a peak at your article. Great write up 👍🏼

 

Thanks so much Robert! Hope I've got some time to publish part 2 soon

 

I'm glad this was linked because the article was missing the crucial step of adding --ext js,jsx,ts,tsx to the npm run script.

 

In VSCode I get a ts error like this photo (thepracticaldev.s3.amazonaws.com/i...) but if I run eslint by itself it does not report on it.

pwd$ ./node_modules/.bin/eslint --fix src/
pwd$

So my pre commit hooks do not bail out correctly as they always seem to pass. Surely I must be missing something?

 

ESlint doesn't check for TypeScript errors, so if you want to check for TypeScript errors in your pre commit hook, you'll need to run the tsc --noEmit command in addition to the ESLint command.

Here's a pre commit command that you could use:

"husky": {
    "hooks": {
        "pre-commit": "tsc --noEmit && eslint --fix src/"
    }
},

However, I would suggest using lint-staged so you don't have to run the eslint command on all the files in your src/, but rather only run it on files that are staged to be committed. This will save you time.

"husky": {
    "hooks": {
        "pre-commit": "tsc --noEmit && lint-staged"
    }
},
"lint-staged": {
    "*.{js,ts,tsx,jsx}": [
        "eslint . --fix",
        "git add"
    ]
}
 

Oh well that makes total sense. I though eslint with ts was doing tslint, and I thought tslint would do these kind of checks.

Many thanks, and yeah, I went with the section option:

    "lint-staged": {
        "src/**/*.{tsx,js}": [
            "prettier --single-quote --write",
            "eslint --fix",
            "git add"
        ]
    },

Thank you Robert for the easy-to-follow article & bitten for adding the prettier option.

I was able to get the eslint & prettier set up for my pet project after following this post & the comments.

cshooks / hooks

List of all React hooks using data structures and algorithms

cshooks

All Contributors Known Vulnerabilities

A collection of React Hooks using Computer Science (CS) data structures & algorithms.

Purpose

Mainly to learn CS data structure & algorithms
(and also implement'em in TypeScript).

Hopefully some of the arcane data structures & algorithms help you as well.

Implemented

useTrie

Returns a Trie data structure, which is used to save a list of words to search in memory efficient manner & provide a type-ahead (not yet implemented) functionality.

Contributors

Thanks goes to these wonderful people (emoji key):

This project follows the all-contributors specification. Contributions of any kind welcome!


 

Apparently .eslintrc (as a JSON file) can contain JS-style comments. That's helpful to me, because Visual Studio 2017 seems happiest with JSON rather than JS.

 

Ah interesting, thanks for pointing that out Michael.

 

Nice write up! I'm using something pretty similar in my project, however I have noticed on larger typescript projects that the eslint.autoFixOnSave feature stops working correctly with this setup if I set my eslintrc to point to my tsconfig in parserOptions.

I haven't figured out exactly whats going on, it could be something funky in my tsconfig

 

Not sure what could be causing your issue. I’ve got this setup working for a large project written in TypeScript and it works without issue.

 

Seems to maybe be a performance issue with @typescript-eslint/parser. It only affects some projects and they are still investigating the root issue.

github.com/typescript-eslint/types...

 

Thank you, Robert. This was quite educational.

Especially because I've recently moved to TSLint without knowing about the the TypeScript 2019 roadmap and being a TypeScript newbie :).

 

Ya, I was using TSLint before recently switching to ESLint for TypeScript. TSLint works well, but I found myself missing certain rules that were available in ESLint, but not TSLint.

 

Hi Robert, i'm trying to implement typescript and eslint to my existing nextjs project
Somehow I got error:

Cannot read config file: /Users/jason/project/<ProjectName>/node_modules/@typescript-eslint/eslint-plugin/dist/index.js Error: Cannot find module 'typescript' Referenced from: /Users/jason/project/<ProjectName>/.eslintrc.js

and for now every warning is still coming from tslint (as the warning come with ts(<code>))

I don't have idea why is that happen, can u help me or at least give me some insight?

 

The error says you don't have typescript installed as a project dependency.

Also, tslint will continue displaying errors if you have a tslint configuration file in your repository, so just get rid of that file. It might be worth disabling tslint in your VSCode settings (you can disable it for your workplace settings only rather than globally under your user settings).

Hopefully that helps!

 

Thanks for the article I've just converted my TS node project to this setup!

 
 

Very helpful! I've used typescript but I'm a newbie to eslint and prettier. I understand them much better now. Thanks!

 
 
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