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explicit-timer-delay: Add rule
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‎docs/rules/explicit-timer-delay.md‎

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# Enforce or disallow explicit `delay` argument for `setTimeout()` and `setInterval()`
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💼 This rule is enabled in the following [configs](https://github.com/sindresorhus/eslint-plugin-unicorn#recommended-config): ✅ `recommended`, ☑️ `unopinionated`.
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🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
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<!-- end auto-generated rule header -->
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<!-- Do not manually modify this header. Run: `npm run fix:eslint-docs` -->
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When using [`setTimeout()`](https://developer.mozilla.org/en-US/docs/Web/API/setTimeout) or [`setInterval()`](https://developer.mozilla.org/en-US/docs/Web/API/setInterval), the `delay` parameter is optional and defaults to `0`. This rule allows you to enforce whether the `delay` argument should always be explicitly provided or omitted when it's `0`.
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This provides flexibility for different team preferences:
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- `"always"` (default): Require explicit `delay` argument for clarity
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- `"never"`: Disallow explicit `0` delay (prefer implicit default)
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## Examples
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### With `"always"` (default)
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```js
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// ❌
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setTimeout(() => console.log('Hello'));
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setInterval(callback);
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window.setTimeout(() => console.log('Hello'));
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globalThis.setInterval(callback);
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// ✅
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setTimeout(() => console.log('Hello'), 0);
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setInterval(callback, 0);
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setTimeout(() => console.log('Hello'), 1000);
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window.setTimeout(() => console.log('Hello'), 0);
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globalThis.setInterval(callback, 100);
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```
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### With `"never"`
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```js
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// ❌
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setTimeout(() => console.log('Hello'), 0);
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setInterval(callback, 0);
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window.setTimeout(() => console.log('Hello'), 0);
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globalThis.setInterval(callback, 0);
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// ✅
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setTimeout(() => console.log('Hello'));
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setInterval(callback);
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setTimeout(() => console.log('Hello'), 1000);
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window.setTimeout(() => console.log('Hello'));
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globalThis.setInterval(callback, 100);
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```
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## Options
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Type: `string`
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Values: `"always"` (default) | `"never"`
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### `"always"`
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Requires an explicit `delay` argument for all `setTimeout()` and `setInterval()` calls.
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```json
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{
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"unicorn/explicit-timer-delay": ["error", "always"]
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}
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```
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### `"never"`
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Disallows an explicit `delay` argument when it's `0`. Non-zero delays are still allowed.
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```json
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{
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"unicorn/explicit-timer-delay": ["error", "never"]
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}
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```

‎readme.md‎

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| [escape-case](docs/rules/escape-case.md) | Require escape sequences to use uppercase or lowercase values. | ✅ ☑️ | 🔧 | |
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| [expiring-todo-comments](docs/rules/expiring-todo-comments.md) | Add expiration conditions to TODO comments. | ✅ ☑️ | | |
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| [explicit-length-check](docs/rules/explicit-length-check.md) | Enforce explicitly comparing the `length` or `size` property of a value. | ✅ | 🔧 | 💡 |
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| [explicit-timer-delay](docs/rules/explicit-timer-delay.md) | Enforce or disallow explicit `delay` argument for `setTimeout()` and `setInterval()`. | ✅ ☑️ | 🔧 | |
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| [filename-case](docs/rules/filename-case.md) | Enforce a case style for filenames. | ✅ | | |
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| [import-style](docs/rules/import-style.md) | Enforce specific import styles per module. | ✅ ☑️ | | |
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| [new-for-builtins](docs/rules/new-for-builtins.md) | Enforce the use of `new` for all builtins, except `String`, `Number`, `Boolean`, `Symbol` and `BigInt`. | ✅ ☑️ | 🔧 | 💡 |

‎rules/explicit-timer-delay.js‎

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import {isLiteral} from './ast/index.js';
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const MODE_ALWAYS = 'always';
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const MODE_NEVER = 'never';
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const MESSAGE_ID_MISSING_DELAY = 'missing-delay';
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const MESSAGE_ID_REDUNDANT_DELAY = 'redundant-delay';
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const messages = {
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[MESSAGE_ID_MISSING_DELAY]: '`{{name}}` should have an explicit delay argument.',
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[MESSAGE_ID_REDUNDANT_DELAY]: '`{{name}}` should not have an explicit delay of `0`.',
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};
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const timerFunctions = new Set(['setTimeout', 'setInterval']);
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/**
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Check if a call expression is a timer function call.
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@param {import('estree').CallExpression} node - The call expression node.
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@param {import('eslint').SourceCode} sourceCode
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@returns {{isTimer: boolean, name?: string}} Object with isTimer flag and function name.
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*/
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const checkTimerCall = (node, sourceCode) => {
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const {callee} = node;
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if (
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callee.type === 'Identifier'
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&& timerFunctions.has(callee.name)
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&& sourceCode.isGlobalReference(callee)
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) {
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return {isTimer: true, name: callee.name};
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}
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if (
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callee.type === 'MemberExpression'
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&& !callee.computed
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&& callee.property.type === 'Identifier'
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&& timerFunctions.has(callee.property.name)
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) {
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const {object} = callee;
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if (
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object.type === 'Identifier'
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&& sourceCode.isGlobalReference(object)
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) {
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return {isTimer: true, name: callee.property.name};
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}
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return {isTimer: false};
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}
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return {isTimer: false};
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};
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/**
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Check if the delay argument is explicitly zero.
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@param {import('estree').Node} node - The argument node.
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@returns {boolean} True if the argument is zero.
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*/
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const isZeroDelay = node =>
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isLiteral(node, 0)
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|| (node.type === 'UnaryExpression' && node.operator === '-' && isLiteral(node.argument, 0));
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/** @param {import('eslint').Rule.RuleContext} context */
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const create = context => {
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const mode = context.options[0] || MODE_ALWAYS;
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const {sourceCode} = context;
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context.on('CallExpression', node => {
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if (node.optional) {
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return;
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}
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const {isTimer, name} = checkTimerCall(node, sourceCode);
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if (!isTimer) {
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return;
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}
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const {arguments: arguments_} = node;
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const hasDelayArgument = arguments_.length >= 2;
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if (mode === MODE_ALWAYS && !hasDelayArgument) {
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if (arguments_.length === 0) {
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return;
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}
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const problem = {
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node,
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messageId: MESSAGE_ID_MISSING_DELAY,
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data: {name},
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};
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const [firstArgument] = arguments_;
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if (firstArgument && firstArgument.type !== 'SpreadElement') {
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problem.fix = fixer => fixer.insertTextAfter(firstArgument, ', 0');
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}
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return problem;
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}
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if (mode === MODE_NEVER && hasDelayArgument) {
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const delayArgument = arguments_[1];
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if (isZeroDelay(delayArgument)) {
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return {
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node: delayArgument,
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messageId: MESSAGE_ID_REDUNDANT_DELAY,
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data: {name},
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fix(fixer) {
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const firstArgument = arguments_[0];
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const [, firstArgumentEnd] = sourceCode.getRange(firstArgument);
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const [delayArgumentStart] = sourceCode.getRange(delayArgument);
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return fixer.removeRange([firstArgumentEnd, delayArgumentStart + sourceCode.getText(delayArgument).length]);
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},
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};
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}
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}
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});
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};
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const schema = [
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{
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enum: [MODE_ALWAYS, MODE_NEVER],
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},
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];
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/** @type {import('eslint').Rule.RuleModule} */
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const config = {
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create,
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meta: {
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type: 'suggestion',
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docs: {
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description: 'Enforce or disallow explicit `delay` argument for `setTimeout()` and `setInterval()`.',
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recommended: 'unopinionated',
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},
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fixable: 'code',
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schema,
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defaultOptions: [MODE_ALWAYS],
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messages,
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},
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};
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export default config;

‎rules/index.js‎

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export {default as 'escape-case'} from './escape-case.js';
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export {default as 'expiring-todo-comments'} from './expiring-todo-comments.js';
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export {default as 'explicit-length-check'} from './explicit-length-check.js';
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export {default as 'explicit-timer-delay'} from './explicit-timer-delay.js';
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export {default as 'filename-case'} from './filename-case.js';
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export {default as 'import-style'} from './import-style.js';
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export {default as 'new-for-builtins'} from './new-for-builtins.js';

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