Add markdownlint (#1597)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

.markdownlint.json

@@ -0,0 +1,8 @@
+{
+	"line-length": false,
+	"no-duplicate-heading": false,
+	"no-hard-tabs": false,
+	"ul-style": {
+		"style": "dash"
+	}
+}

.markdownlintignore

@@ -0,0 +1,2 @@
+node_modules
+test/snapshots

docs/rules/consistent-function-scoping.md

@@ -4,7 +4,6 @@
 
 A function definition should be placed as close to the top-level scope as possible without breaking its captured values. This improves readability, [directly improves performance](https://stackoverflow.com/a/81329/207247) and allows JavaScript engines to [better optimize performance](https://ponyfoo.com/articles/javascript-performance-pitfalls-v8#optimization-limit).
 
-
 ## Fail
 
 ```js
@@ -24,7 +23,6 @@ function doFoo(foo) {
 }
 ```
 
-
 ## Pass
 
 ```js

docs/rules/custom-error-definition.md

@@ -6,7 +6,6 @@
 
 Enforces the only valid way of `Error` subclassing. It works with any super class that ends in `Error`.
 
-
 ## Fail
 
 ```js
@@ -21,7 +20,6 @@ class CustomError extends Error {
 
 The `this.message` assignment is useless as it's already set via the `super()` call.
 
-
 ```js
 class CustomError extends Error {
 	constructor(message) {
@@ -34,7 +32,6 @@ class CustomError extends Error {
 
 Pass the error message to `super()` instead of setting `this.message`.
 
-
 ```js
 class CustomError extends Error {
 	constructor(message) {
@@ -45,7 +42,6 @@ class CustomError extends Error {
 
 No `name` property set. The name property is needed so the error shows up as `[CustomError: foo]` and not `[Error: foo]`.
 
-
 ```js
 class CustomError extends Error {
 	constructor(message) {
@@ -57,7 +53,6 @@ class CustomError extends Error {
 
 Use a string literal to set the `name` property as it will not change after minifying.
 
-
 ```js
 class CustomError extends Error {
 	constructor(message) {
@@ -69,7 +64,6 @@ class CustomError extends Error {
 
 The `name` property should be set to the class name.
 
-
 ```js
 class foo extends Error {
 	constructor(message) {
@@ -81,7 +75,6 @@ class foo extends Error {
 
 The class name is invalid. It should be capitalized and end with `Error`. In this case it should be `FooError`.
 
-
 ## Pass
 
 ```js

docs/rules/error-message.md

@@ -4,7 +4,6 @@
 
 This rule enforces a `message` value to be passed in when creating an instance of a built-in [`Error`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) object, which leads to more readable and debuggable code.
 
-
 ## Fail
 
 ```js
@@ -23,7 +22,6 @@ throw new TypeError();
 const error = new AggregateError(errors);
 ```
 
-
 ## Pass
 
 ```js

docs/rules/escape-case.md

@@ -6,7 +6,6 @@
 
 Enforces defining escape sequence values with uppercase characters rather than lowercase ones. This promotes readability by making the escaped value more distinguishable from the identifier.
 
-
 ## Fail
 
 ```js
@@ -16,7 +15,6 @@ const foo = '\u{1d306}';
 const foo = '\ca';
 ```
 
-
 ## Pass
 
 ```js

docs/rules/explicit-length-check.md

@@ -156,9 +156,9 @@ You can define your preferred way of checking non-zero length by providing a `no
 The `non-zero` option can be configured with one of the following:
 
 - `greater-than` (default)
-	- Enforces non-zero to be checked with: `foo.length > 0`
+  - Enforces non-zero to be checked with: `foo.length > 0`
 - `not-equal`
-	- Enforces non-zero to be checked with: `foo.length !== 0`
+  - Enforces non-zero to be checked with: `foo.length !== 0`
 
 ## Unsafe to fix case
 

docs/rules/filename-case.md

@@ -8,6 +8,8 @@ Files named `index.js`, `index.mjs`, `index.cjs`, `index.ts`, `index.tsx`, `inde
 
 Characters in the filename except `a-z`, `A-Z`, `0-9`, `-`, `_` and `$` are ignored.
 
+## Cases
+
 ### `kebabCase`
 
 - `foo-bar.js`
@@ -32,7 +34,6 @@ Characters in the filename except `a-z`, `A-Z`, `0-9`, `-`, `_` and `$` are igno
 - `FooBar.Test.js`
 - `FooBar.TestUtils.js`
 
-
 ## Options
 
 ### case
@@ -80,6 +81,7 @@ When a string is given, it's interpreted as a regular expressions inside a strin
 Sometimes you may have non-standard filenames in a project. This option lets you ignore those files.
 
 For example:
+
 - Vendor packages that are not published and was copy-pasted.
 - Ignore some files when you use [eslint-plugin-markdown](https://github.com/eslint/eslint-plugin-markdown), for example `README.md`.
 - Some tools may require special names for some files.

docs/rules/import-index.md

@@ -6,7 +6,6 @@
 
 Enforces importing index file with `.` instead of `./`, `./index` or `./index.js`.
 
-
 ## Fail
 
 ```js
@@ -41,7 +40,6 @@ import m from './';
 import m from './index';
 ```
 
-
 ## Pass
 
 ```js
@@ -64,7 +62,6 @@ const m = require('@foo/bar');
 import m from '.';
 ```
 
-
 ## Options
 
 ### ignoreImports

docs/rules/import-style.md

@@ -5,6 +5,7 @@
 Sometimes a module contains unrelated functions, like `util`, thus it is a good practice to enforce destructuring or named imports here. Other times, in modules like `path`, it is good to use default import as they have similar functions, all likely to be utilized.
 
 This rule defines 4 import styles:
+
 - `unassigned` - `import 'foo'` or `require('foo')`
 - `default` - `import path from 'path'` or `const path = require('path')`
 - `namespace` - `import * as path from 'path'` or `const path = require('path')`
@@ -37,11 +38,13 @@ Type: `object`
 You can extend default import styles per module by passing the `styles` option.
 
 Default options per module are:
+
 - `util` - `named` only
 - `path` - `default` only
 - `chalk` - `default` only
 
 The example below:
+
 - Disables any restrictions on the `util` module imports.
 - Allows `named` import (leaving `default` allowed too) from the `path` module (by default only `default` import of `path` is allowed).
 

docs/rules/no-abusive-eslint-disable.md

@@ -33,7 +33,6 @@ console.log(message); // `message` is not defined, but it won't be reported
 
 This rule enforces specifying the rules to disable. If you want to disable ESLint on a file altogether, you should ignore it through [`.eslintignore`](https://eslint.org/docs/user-guide/configuring#ignoring-files-and-directories) for ESLint or through the [`ignores` property](https://github.com/xojs/xo#ignores) in `package.json` for `XO`.
 
-
 ## Fail
 
 ```js
@@ -46,7 +45,6 @@ console.log(message); // eslint-disable-line
 console.log(message);
 ```
 
-
 ## Pass
 
 ```js

docs/rules/no-array-reduce.md

@@ -54,6 +54,7 @@ for (const element of array) {
 	result += element;
 }
 ```
+
 ## Options
 
 ### allowSimpleOperations

docs/rules/no-console-spaces.md

@@ -6,7 +6,6 @@
 
 The [`console.log()` method](https://developer.mozilla.org/en-US/docs/Web/API/Console/log) and similar methods joins the parameters with a space, so adding a leading/trailing space to a parameter, results in two spaces being added.
 
-
 ## Fail
 
 ```js
@@ -22,7 +21,6 @@ console.warn('abc ', 'def');
 console.error('abc ', 'def');
 ```
 
-
 ## Pass
 
 ```js

docs/rules/no-for-loop.md

@@ -10,7 +10,6 @@ Off-by-one errors are one of the most common bugs in software. [Swift actually r
 
 This rule is fixable unless index or element variables were used outside of the loop.
 
-
 ## Fail
 
 ```js
@@ -20,7 +19,6 @@ for (let index = 0; index < array.length; index++) {
 }
 ```
 
-
 ## Pass
 
 ```js

docs/rules/no-hex-escape.md

@@ -6,15 +6,13 @@
 
 Enforces a convention of using [Unicode escapes](https://mathiasbynens.be/notes/javascript-escapes#unicode) instead of [hexadecimal escapes](https://mathiasbynens.be/notes/javascript-escapes#hexadecimal) for consistency and clarity.
 
-
 ## Fail
 
 ```js
 const foo = '\x1B';
 const foo = `\x1B${bar}`;
 ```
 
-
 ## Pass
 
 ```js

docs/rules/no-instanceof-array.md

@@ -6,15 +6,13 @@
 
 The `instanceof Array` check doesn't work across realms/contexts, for example, frames/windows in browsers or the `vm` module in Node.js.
 
-
 ## Fail
 
 ```js
 array instanceof Array;
 [1,2,3] instanceof Array;
 ```
 
-
 ## Pass
 
 ```js

docs/rules/no-keyword-prefix.md

@@ -11,7 +11,6 @@ const newFoo = 'foo';
 const classFoo = 'foo';
 ```
 
-
 ## Pass
 
 ```js
@@ -21,7 +20,6 @@ const new_foo = 'foo';
 const fooNew = 'foo';
 ```
 
-
 ## Options
 
 ### `disallowedPrefixes`

docs/rules/no-nested-ternary.md

@@ -6,23 +6,20 @@
 
 Improved version of the [`no-nested-ternary`](https://eslint.org/docs/rules/no-nested-ternary) ESLint rule, which allows cases where the nested ternary is only one level and wrapped in parens.
 
-
 ## Fail
 
 ```js
 const foo = i > 5 ? i < 100 ? true : false : true;
 const foo = i > 5 ? true : (i < 100 ? true : (i < 1000 ? true : false));
 ```
 
-
 ## Pass
 
 ```js
 const foo = i > 5 ? (i < 100 ? true : false) : true;
 const foo = i > 5 ? (i < 100 ? true : false) : (i < 100 ? true : false);
 ```
 
-
 ## Partly fixable
 
 This rule is only fixable when the nesting is up to one level. The rule will wrap the nested ternary in parens:
@@ -37,7 +34,6 @@ will get fixed to
 const foo = i > 5 ? (i < 100 ? true : false) : true
 ```
 
-
 ## Disabling ESLint `no-nested-ternary`
 
 We recommend disabling the ESLint `no-nested-ternary` rule in favor of this one:

docs/rules/no-new-buffer.md

@@ -12,7 +12,7 @@ Enforces the use of [Buffer.from](https://nodejs.org/api/buffer.html#buffer_clas
 const buffer = new Buffer('7468697320697320612074c3a97374', 'hex');
 ```
 
-```
+```js
 const buffer = new Buffer([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
 ```
 

docs/rules/no-object-as-default-parameter.md

@@ -18,7 +18,6 @@ function foo({a} = {a: false}) {}
 const abc = (foo = {a: false, b: 123}) => {};
 ```
 
-
 ## Pass
 
 ```js

docs/rules/no-process-exit.md

@@ -4,14 +4,12 @@
 
 This rule is an extension to ESLint's [`no-process-exit` rule](https://eslint.org/docs/rules/no-process-exit), that allows `process.exit()` to be called in files that start with a [hashbang](https://en.wikipedia.org/wiki/Shebang_(Unix)) → `#!/usr/bin/env node`. It also allows `process.exit()` to be called in `process.on('<event>', func)` event handlers and in files that imports `worker_threads`.
 
-
 ## Fail
 
 ```js
 process.exit(0);
 ```
 
-
 ## Pass
 
 ```js

docs/rules/no-unreadable-array-destructuring.md

@@ -24,7 +24,6 @@ const [,,,, foo] = parts;
 const [,,...rest] = parts;
 ```
 
-
 ## Pass
 
 ```js

docs/rules/no-unsafe-regex.md

@@ -4,7 +4,6 @@
 
 Uses [safe-regex](https://github.com/substack/safe-regex) to disallow potentially [catastrophic](https://regular-expressions.mobi/catastrophic.html) [exponential-time](https://perlgeek.de/blog-en/perl-tips/in-search-of-an-exponetial-regexp.html) regular expressions.
 
-
 ## Fail
 
 ```js
@@ -17,7 +16,6 @@ const regex = /(a+){2}y/;
 const regex = /(.*){1,32000}[bc]/;
 ```
 
-
 ## Pass
 
 ```js