An Optioned Guide to ESLint

ESLint is a powerful and versatile tool. I myself only use eslint for problems coming from JavaScript design. Thus, I can have a short rule list.

No Formatting Rule

Use deno fmt or prettier instead.

I use deno fmt or prettier with its default options, without any configuration.

deno fmt is faster, while prettier supports more formats.

Prettier also helps on some non-formatting lint rules. For example, eslint’s curly rule helps to avoid misleading code:

if (condition)

However, prettier will format the above code as below to avoid the above issue:

if (condition) do_something();

In the code sample above, I use snake_case for function names. The Python community favors snake_case:

Function names should be lowercase, with words separated by underscores as necessary to improve readability.

Variable names follow the same convention as function names.

mixedCase is allowed only in contexts where that’s already the prevailing style (e.g. threading.py), to retain backwards compatibility.


However, mixedCase is prevailing in the JavaScript/TypeScript community. Thus, I use mixedCase for exported names.

TypeScript Can Detect Lots of Errors

TypeScript can detect a lot of problems, and it is usually faster.

For example, the array-callback-return rule is unnecessary, because if I accidentally forget to write return statement in array mapping function, it tends to trigger a type error. eqeqeq is another example of an unnecessary rule, since TypeScript complains when you are comparing two values of different types.

TypeScript also has other helpful checks like noFallthroughCasesInSwitch.

So just extend one of strictest tsconfig base.

Only Include Obvious Rules

Do not include rules such as no-new-object and no-nested-ternary, which are merely personal choice of programming style.

So here is the five ESLint rules I use:

"rules": {
    "prefer-arrow-callback": "error", // avoid the evil `this`
    "no-multi-assign": "error", // no `a = b = c = 1`
    "no-var": "error", // use `const` and `let` instead of `var`
    "prefer-const": "error", // use `const` when there is no reassignment
    "no-param-reassign": "error", // use nonreassignable function parameters

Note that the default ESLint configuration file generated via @eslint/config includes a lot of recommended rules (extends). I do not use npm init @eslint/config and add dependencies by hand:

ni -D eslint @typescript-eslint/eslint-plugin @typescript-eslint/parser

ESLint configuration file example:

  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"],
  "rules": {
    "prefer-arrow-callback": "error", // avoid the evil `this`
    "no-multi-assign": "error", // no `a = b = c = 1`
    "no-var": "error", // use `const` and `let` instead of `var`
    "prefer-const": "error", // use `const` when there is no reassignment
    "no-param-reassign": "error" // use nonreassignable function parameters


Rome and quick-lint-ls are faster alternatives to ESLint. Rome does not support Svelte, and quick-lint-ls does not support TypeScript. Therefore, I still use ESLint.