Using ESLint to Format Javascript Code

Using ESLint to Format Javascript Code

For JavaScript code we use both:

• eslint - linting tool

• Prettier - formatting tool

These tools can be used via the command line or right in your code editor.

Via the Command Line

After editing some JavaScript code, navigate to the comm/ directory. (The following commands need to be run from the comm/ directory so that Prettier will use the comm/.prettierignore file, and not the .prettierignore file in the directory just above comm/. See Prettier issue 4081.)

For a single file, run this command, which will attempt to automatically fix any linting or formatting problems:

$ ../mach lint path/to/a/file.js --fix

Or for all the files in a given directory:

$ ../mach lint path/to/a/directory/ --fix

To simply report any problems but not attempt to automatically fix them, just omit the --fix flag:

$ ../mach lint path/to/a/file.js

In a Code Editor

Most popular code editors offer plugins for eslint and Prettier. We highly recommend installing a plugin for eslint and a plugin for Prettier so you can lint and format your code as you are editing it. Issues will be highlighted as you type and you can have Prettier format your code with a few key strokes.

Here are links to plugins for various editors:

• eslint plugins for various editors

• Prettier plugins for various editors

Some of us on the Thunderbird team use the VS Code editor with these plugins:

• Prettier - Code formatter

  VS Code plugin by Esben Petersen

• ESLint

  VS Code plugin by Dirk Baeumer

More Details

• 'Linting' on firefox-source-docs

• 'Formatting JS Code With Prettier and eslint' on MDN