• https://eslint.org/docs/rules/array-callback-return (v2.0.0) (not taken, see known limitation)
• http://eslint.org/docs/rules/getter-return (v4.2.0)
• https://eslint.org/docs/rules/implicit-arrow-linebreak (v4.12.0) (not needed)
• https://eslint.org/docs/rules/no-var (v0.12.0)
• https://eslint.org/docs/rules/eol-last (v0.7.1) (already present)
• https://eslint.org/docs/rules/no-buffer-constructor (v4.0.0) (already present)
• https://eslint.org/docs/rules/prefer-rest-params (v2.0.0)
• https://eslint.org/docs/rules/prefer-spread (v1.0.0)
• https://eslint.org/docs/rules/no-async-promise-executor (v5.3.0)
• https://eslint.org/docs/rules/require-atomic-updates (v5.3.0)
• https://eslint.org/docs/rules/no-misleading-character-class (v5.3.0)

ESLint 5.x.x migration guide

This will allow the primary config to move on to ES6 features.

This might not be comprehensive, but...

• move from .eslintrc to .eslintrc.js
• no-arrow-condition is replaced by no-constant-condition and no-confusing-arrow
• no-empty-label is replaced by no-labels with {"allowLoop": true, "allowSwitch": true} option
• space-after-keywords is replaced by keyword-spacing
• space-before-keywords is replaced by keyword-spacing
• space-return-throw-case is replaced by keyword-spacing

New rules to use

• array-callback-return
• keyword-spacing
• no-implicit-globals
• no-new-symbol
• no-self-assign
• no-useless-constructor
• no-whitespace-before-property
• one-var-declaration-per-line
• template-curly-spacing
• yield-star-spacing

Consider these rules:

• no-useless-escape
• no-duplicate-imports
• no-unsafe-finally
• no-useless-computed-key
• object-property-newline with allowMultiplePropertiesPerLine enabled
• unicode-bom with never setting
• object-curly-newline with multiline: true
• rest-spread-spacing with never setting

bin/belly-button.js wraps lib/cli.js. Need to finalize the interface of the CLI run() function. Specifically, how will errors, stdout, stderr, and the process exit code be passed around.

Rules to possibly enable

• http://eslint.org/docs/rules/class-methods-use-this (v3.4.0)
• http://eslint.org/docs/rules/symbol-description (v3.4.0)
• http://eslint.org/docs/rules/prefer-numeric-literals (v3.5.0)
• http://eslint.org/docs/rules/no-useless-return (v3.9.0)
• http://eslint.org/docs/rules/no-return-await (v3.10.0)
• http://eslint.org/docs/rules/require-await (v3.11.0)
• http://eslint.org/docs/rules/capitalized-comments (v3.11.0)
• http://eslint.org/docs/rules/no-multi-assign (v3.14.0)
• http://eslint.org/docs/rules/no-compare-neg-zero (v3.17.0)
• http://eslint.org/docs/rules/no-buffer-constructor (v4.0.0)
• http://eslint.org/docs/rules/switch-colon-spacing (v4.0.0)

Allow one variable per const/let/var.

Currently marked with a TODO comment

no-use-before-define: [2, "nofunc"] will enforce for variables, but allow functions to be hoisted.

CLIEngine is being replaced by ESLint in v7.0.0.

See https://eslint.org/blog/2020/02/whats-coming-in-eslint-7.0.0#eslint-class-replacing-cliengine-class and eslint/rfcs#40.

Likely post v1.0.0

This is a new rule, which I'm assuming will show up in [email protected]

Things that might be worth incorporating:

• New es2022 environment. Introduced in 8.9.0.
• New no-unused-private-class-members rule. Introduced in 8.1.0.
• New prefer-object-has-own rule. Introduced in 8.5.0.
• New no-constant-binary-expression rule. Introduced in 8.14.0.

100% code coverage achieved in a64a277. However, at least one of the tests needs to be improved. It is currently marked with a TODO comment.

Things that might be worth incorporating:

• ecmaVersion: 2020 config option. Introduced in v6.2.0.
• reportUnusedDisableDirectives config option. Introduced in v6.3.0.
• enforceForClassMembers option to the computed-property-spacing rule. Introduced in v6.4.0.
• New default-param-last rule. Introduced in v6.4.0.
• New prefer-regex-literals rule. Introduced in v6.4.0.
• New no-constructor-return rule. Introduced in v6.7.0.
• New no-dupe-else-if rule. Introduced in v6.7.0.
• New no-setter-return rule. Introduced in v6.7.0.
• New prefer-exponentiation-operator rule. Introduced in v6.7.0.
• New default-case-last rule. Introduced in v7.0.0.
• New no-useless-backreference rule. Introduced in v7.0.0.
• New no-restricted-exports rule. Introduced in v7.0.0.

Added this in v3.0.0, but as it is configured in belly-button, it prevents:

foo: {
  bar: 'baz'
}

Things that might be worth incorporating:

• New no-loss-of-precision rule. Introduced in 7.1.0.
• New no-unreachable-loop rule. Introduced in 7.3.0.
• New no-unsafe-optional-chaining rule. Introduced in 7.15.0.
• Not new, but no-unused-expressions.

The following rules used by belly-button are deprecated in ESLint core as of v7.0.0:

• handle-callback-err
• no-buffer-constructor
• no-new-require

Enable this in the next major version bump. The rule disregards var, so it's backwards compatible for code written in older versions of ES.

A few rules used in this config are deprecated in http://eslint.org/blog/2016/08/eslint-v3.3.0-released.

Things that might be worth incorporating (as of ESLint v8.25.0):

• New prefer-object-has-own rule. Introduced in 8.5.0. Need to wait for Node 14 to be dropped.
• New no-use-before-define option allowNamedExports. Introduced in 8.17.0.

Right now the behavior is "after", which exceptions for "?" and ":". Remove the exceptions.

Consider changing to {"anonymous": "always", "named": "never"}. This would allow function foo(), while still requiring function () (anonymous vs. named). @arb thoughts?

Thoughts on making import blocked?