README.md

Static Analysis Testing JavaScript Applications

Table of Contents

• 1. Lint JavaScript by configuring and running ESLint
• 2. Format Code by installing and running Prettier
• 3. Configure Prettier
• 4. Disable Unnecessary ESLint Stylistic Rules with eslint-config-prettier
• 5. Validate all files are formatted when linting
• 6. Avoid Common Errors with Flow Type Definitions
• 7. Validate Code in a pre-commit git Hook with husky
• 8. Auto-format all files and validate relevant files in a precommit script with lint-staged

1. Lint JavaScript by configuring and running ESLint

$ npm run lint

Eslint rules with error will exit the process and fail a build.

Eslint rules with warn will continue to run the process and not fail a build.

Eslint rules with off will ignore the rule entirely.

One can extend one's eslint config using the extends property. eslint:recommended is a built-in config.

The env property can be used to set the environment against which files should be evaluated.

2. Format Code by installing and running Prettier

prettier can be used to format code in files via CLI:

$ prettier --write path/to/files

prettier can be used to format markdown and graphql, too.

3. Configure Prettier

prettier allows for a .prettierignore to ignore formatting of generated files

4. Disable Unnecessary ESLint Stylistic Rules with eslint-config-prettier

extended eslint configs take precedence from the end of the array.

rules in the the eslint config take precedence over any extensions.

5. Validate all files are formatted when linting

prettier can be run with a --list-different flag which exits with a non-zero code if there are any files that are not formatted correctly. This can be used with ghooks to ensure all team members are using prettier.

npm scripts can forward command line arguments to each other using the -- operator:

  ...
  "scripts": {
    "myscript": "some-command",
    "myscript:alpha": "npm run myscript -- --some-flag"
  }
  ...

$ npm run myscript -- --some-flag

# or
$ npm run myscript:alpha

6. Avoid Common Errors with Flow Type Definitions

Use @flow at the top of files that you want to use flow to make type strict after installing flow-bin as a dev dependency.

7. Validate Code in a pre-commit git Hook with husky

husky works in a similar way to ghooks, except that you add npm scripts to run pre and post-hooks.

8. Auto-format all files and validate relevant files in a precommit script with lint-staged

lint-staged not only allows linters to be run on precommit, but allows one to define commands to be run should linting pass, allowing for repo owners to have autoformatting run and changed files staged without relying on collaborators to have autoformatters enabled.