Creating a React and TypeScript project with linting and automatic code formatting has never been easier. In this post we’ll do this with Create React App 3.

Creating the project

Let’s run the following command to create the project:

npx create-react-app app --typescript

• The npx tool temporarily installs the create-react-app npm package and uses it to create our project
• We’ve called our project app
• We’ve also specified --typescript, which is the bit that tells the tool to set the project up with TypeScript.

The tool will take a minute or so to create the project.

Linting in CRA3

ESLint is the most popular linter in the React community and is automatically installed into a CRA project. CRA3 also configures ESLint to lint TypeScript code - neat!

Note that TSLint has been a popular alternative to ESLint for linting TypeScript code but is now deprecated. More information can be found here.

Configuring Visual Studio Code to lint TypeScript code

CRA has already installed ESLint and configured it for us but we need to tell VS Code to lint TypeScript code. We can do this in our project in a settings.json file with the following settings in a folder called .vscode:

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

The most popular linting extension in VS Code is ESLint and is published by Dirk Baeumer:

Linting errors will now be underlined as well as appearing in the Problems list:

If we want to configure the linting rules, we first add a file called .eslintrc.json in project root folder with the following content:

{
  "extends": "react-app"
}

This file defines the rules that ESLint executes and this simply configures ESLint to execute all the rules that are configured in CRA. We can add additional rules we want to run in a rules field:

{
  "extends": "react-app",
  "rules": {
    "no-debugger": "warn"
  }
}

All the available ESLint rules can be found here.

Adding automatic code formatting

Some of the linting rules that deal with the format of our code (such as semi colons at the end of statements) can be automatically dealt with by a tool like Prettier.

We can install Prettier by executing the following command in the Terminal:

npm install prettier --save-dev

Prettier can take responsibility for the style rules off of ESLint by using the eslint-config-prettier and eslint-plugin-prettier ESLint plugins.

• eslint-config-prettier disables ESLint rules that conflict with Prettier
• eslint-plugin-prettier is a ESLint rule that formats code using Prettier

These can be installed using the following command:

npm install eslint-config-prettier eslint-plugin-prettier --save-dev

The following prettier settings also need to be added to .eslintrc.json:

{
  "extends": ["react-app", "prettier"],
  "plugins": ["prettier"],
  "rules": {
    "prettier/prettier": "error"
  }
}

The formatting rules can be specified in a .prettierrc file in the project root folder. Here’s an example prettier configuration:

{
  "printWidth": 80,
  "singleQuote": true,
  "semi": true,
  "tabWidth": 2,
  "trailingComma": "all"
}

More information can be found on prettier configuration here.

#react