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feat(eslint-plugin): added new rule no-dynamic-delete (typescript-eslint#565)
 Co-authored-by: Josh Goldberg <josh@fullscreenmario.com> Co-authored-by: Brad Zacher <brad.zacher@gmail.com>
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‎packages/eslint-plugin/README.md

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@@ -160,6 +160,7 @@ Then you should add `airbnb` (or `airbnb-base`) to your `extends` section of `.e
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| [`@typescript-eslint/member-naming`](./docs/rules/member-naming.md) | Enforces naming conventions for class members by visibility | | | |
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| [`@typescript-eslint/member-ordering`](./docs/rules/member-ordering.md) | Require a consistent member declaration order | | | |
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| [`@typescript-eslint/no-array-constructor`](./docs/rules/no-array-constructor.md) | Disallow generic `Array` constructors | :heavy_check_mark: | :wrench: | |
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| [`@typescript-eslint/no-dynamic-delete`](./docs/rules/no-dynamic-delete.md) | Bans usage of the delete operator with computed key expressions | | :wrench: | |
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| [`@typescript-eslint/no-empty-function`](./docs/rules/no-empty-function.md) | Disallow empty functions | :heavy_check_mark: | | |
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| [`@typescript-eslint/no-empty-interface`](./docs/rules/no-empty-interface.md) | Disallow the declaration of empty interfaces | :heavy_check_mark: | | |
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| [`@typescript-eslint/no-explicit-any`](./docs/rules/no-explicit-any.md) | Disallow usage of the `any` type | :heavy_check_mark: | :wrench: | |

‎packages/eslint-plugin/ROADMAP.md

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@@ -60,7 +60,7 @@
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| [`no-duplicate-super`] | 🌟 | [`constructor-super`][constructor-super] |
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| [`no-duplicate-switch-case`] | 🌟 | [`no-duplicate-case`][no-duplicate-case] |
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| [`no-duplicate-variable`] | 🌟 | [`no-redeclare`][no-redeclare] |
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| [`no-dynamic-delete`] | 🛑 | N/A |
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| [`no-dynamic-delete`] | ✅ | [`@typescript-eslint/no-dynamic-delete`] |
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| [`no-empty`] | 🌟 | [`no-empty`][no-empty] |
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| [`no-eval`] | 🌟 | [`no-eval`][no-eval] |
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| [`no-floating-promises`] | ✅ | [`@typescript-eslint/no-floating-promises`] |
@@ -613,6 +613,7 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
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[`@typescript-eslint/member-delimiter-style`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/member-delimiter-style.md
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[`@typescript-eslint/prefer-for-of`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/prefer-for-of.md
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[`@typescript-eslint/no-array-constructor`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-array-constructor.md
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[`@typescript-eslint/no-dynamic-delete`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-dynamic-delete.md
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[`@typescript-eslint/prefer-function-type`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/prefer-function-type.md
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[`@typescript-eslint/prefer-readonly`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/prefer-readonly.md
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[`@typescript-eslint/require-await`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/require-await.md

‎packages/eslint-plugin/docs/rules/no-dynamic-delete.md

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# Disallow the delete operator with computed key expressions (no-dynamic-delete)
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Deleting dynamically computed keys can be dangerous and in some cases not well optimized.
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## Rule Details
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Using the `delete` operator on keys that aren't runtime constants could be a sign that you're using the wrong data structures.
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Using `Object`s with added and removed keys can cause occasional edge case bugs, such as if a key is named `"hasOwnProperty"`.
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Consider using a `Map` or `Set` if you’re storing collections of objects.
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Examples of **correct** code wth this rule:
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```ts
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const container: { [i: string]: number } = {
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/* ... */
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};
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// Constant runtime lookups by string index
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delete container.aaa;
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// Constants that must be accessed by []
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delete container[7];
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delete container['-Infinity'];
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```
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Examples of **incorrect** code with this rule:
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```ts
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// Can be replaced with the constant equivalents, such as container.aaa
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delete container['aaa'];
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delete container['Infinity'];
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// Dynamic, difficult-to-reason-about lookups
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const name = 'name';
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delete container[name];
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delete container[name.toUpperCase()];
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```
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## When Not To Use It
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When you know your keys are safe to delete, this rule can be unnecessary.
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Some environments such as older browsers might not support `Map` and `Set`.
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Do not consider this rule as performance advice before profiling your code's bottlenecks.
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Even repeated minor performance slowdowns likely do not significantly affect your application's general perceived speed.
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## Related to
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- TSLint: [no-dynamic-delete](https://palantir.github.io/tslint/rules/no-dynamic-delete)

‎packages/eslint-plugin/src/configs/all.json

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"@typescript-eslint/member-ordering": "error",
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"no-array-constructor": "off",
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"@typescript-eslint/no-array-constructor": "error",
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"@typescript-eslint/no-dynamic-delete": "error",
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"no-empty-function": "off",
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"@typescript-eslint/no-empty-function": "error",
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"@typescript-eslint/no-empty-interface": "error",

‎packages/eslint-plugin/src/rules/index.ts

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@@ -18,6 +18,7 @@ import memberDelimiterStyle from './member-delimiter-style';
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import memberNaming from './member-naming';
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import memberOrdering from './member-ordering';
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import noArrayConstructor from './no-array-constructor';
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import noDynamicDelete from './no-dynamic-delete';
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import noEmptyFunction from './no-empty-function';
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import noEmptyInterface from './no-empty-interface';
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import noExplicitAny from './no-explicit-any';
@@ -85,6 +86,7 @@ export default {
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'member-naming': memberNaming,
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'member-ordering': memberOrdering,
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'no-array-constructor': noArrayConstructor,
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'no-dynamic-delete': noDynamicDelete,
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'no-empty-function': noEmptyFunction,
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'no-empty-interface': noEmptyInterface,
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'no-explicit-any': noExplicitAny,

‎packages/eslint-plugin/src/rules/no-dynamic-delete.ts

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import {
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TSESTree,
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AST_NODE_TYPES,
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TSESLint,
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} from '@typescript-eslint/experimental-utils';
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import * as tsutils from 'tsutils';
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import * as util from '../util';
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export default util.createRule({
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name: 'no-dynamic-delete',
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meta: {
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docs: {
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category: 'Best Practices',
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description:
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'Bans usage of the delete operator with computed key expressions',
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recommended: false,
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},
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fixable: 'code',
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messages: {
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dynamicDelete: 'Do not delete dynamically computed property keys.',
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},
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schema: [],
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type: 'suggestion',
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},
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defaultOptions: [],
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create(context) {
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function createFixer(
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member: TSESTree.MemberExpression,
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): TSESLint.ReportFixFunction | undefined {
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if (
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member.property.type === AST_NODE_TYPES.Literal &&
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typeof member.property.value === 'string'
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) {
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return createPropertyReplacement(
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member.property,
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member.property.value,
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);
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}
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if (member.property.type === AST_NODE_TYPES.Identifier) {
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return createPropertyReplacement(member.property, member.property.name);
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}
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return undefined;
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}
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return {
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'UnaryExpression[operator=delete]'(node: TSESTree.UnaryExpression): void {
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if (
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node.argument.type !== AST_NODE_TYPES.MemberExpression ||
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!node.argument.computed ||
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isNecessaryDynamicAccess(
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diveIntoWrapperExpressions(node.argument.property),
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)
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) {
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return;
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}
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context.report({
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fix: createFixer(node.argument),
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messageId: 'dynamicDelete',
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node: node.argument.property,
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});
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},
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};
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function createPropertyReplacement(
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property: TSESTree.Expression,
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replacement: string,
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) {
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return (fixer: TSESLint.RuleFixer): TSESLint.RuleFix =>
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fixer.replaceTextRange(getTokenRange(property), `.${replacement}`);
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}
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function getTokenRange(property: TSESTree.Expression): [number, number] {
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const sourceCode = context.getSourceCode();
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return [
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sourceCode.getTokenBefore(property)!.range[0],
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sourceCode.getTokenAfter(property)!.range[1],
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];
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}
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},
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});
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function diveIntoWrapperExpressions(
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node: TSESTree.Expression,
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): TSESTree.Expression {
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if (node.type === AST_NODE_TYPES.UnaryExpression) {
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return diveIntoWrapperExpressions(node.argument);
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}
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return node;
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}
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function isNecessaryDynamicAccess(property: TSESTree.Expression): boolean {
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if (property.type !== AST_NODE_TYPES.Literal) {
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return false;
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}
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if (typeof property.value === 'number') {
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return true;
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}
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return (
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typeof property.value === 'string' &&
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!tsutils.isValidPropertyAccess(property.value)
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);
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}

‎packages/eslint-plugin/tests/rules/no-dynamic-delete.test.ts

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import path from 'path';
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import rule from '../../src/rules/no-dynamic-delete';
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import { RuleTester } from '../RuleTester';
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const rootDir = path.join(process.cwd(), 'tests/fixtures');
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const ruleTester = new RuleTester({
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parserOptions: {
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ecmaVersion: 2015,
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tsconfigRootDir: rootDir,
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project: './tsconfig.json',
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},
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parser: '@typescript-eslint/parser',
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});
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ruleTester.run('no-dynamic-delete', rule, {
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valid: [
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`const container: { [i: string]: 0 } = {};
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delete container.aaa;`,
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`const container: { [i: string]: 0 } = {};
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delete container.delete;`,
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`const container: { [i: string]: 0 } = {};
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delete container[7];`,
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`const container: { [i: string]: 0 } = {};
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delete container[-7];`,
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`const container: { [i: string]: 0 } = {};
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delete container[+7];`,
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`const container: { [i: string]: 0 } = {};
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delete container['-Infinity'];`,
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`const container: { [i: string]: 0 } = {};
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delete container['+Infinity'];`,
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`const value = 1;
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delete value;`,
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`const value = 1;
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delete -value;`,
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],
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invalid: [
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{
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code: `const container: { [i: string]: 0 } = {};
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delete container['aaa'];`,
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errors: [{ messageId: 'dynamicDelete' }],
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output: `const container: { [i: string]: 0 } = {};
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delete container.aaa;`,
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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delete container [ 'aaa' ] ;`,
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errors: [{ messageId: 'dynamicDelete' }],
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output: `const container: { [i: string]: 0 } = {};
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delete container .aaa ;`,
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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delete container['aa' + 'b'];`,
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errors: [{ messageId: 'dynamicDelete' }],
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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delete container['delete'];`,
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errors: [{ messageId: 'dynamicDelete' }],
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output: `const container: { [i: string]: 0 } = {};
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delete container.delete;`,
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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delete container[-Infinity];`,
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errors: [{ messageId: 'dynamicDelete' }],
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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delete container[+Infinity];`,
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errors: [{ messageId: 'dynamicDelete' }],
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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delete container[NaN];`,
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errors: [{ messageId: 'dynamicDelete' }],
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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delete container['NaN'];`,
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errors: [{ messageId: 'dynamicDelete' }],
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output: `const container: { [i: string]: 0 } = {};
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delete container.NaN;`,
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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delete container [ 'NaN' ] ;`,
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errors: [{ messageId: 'dynamicDelete' }],
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output: `const container: { [i: string]: 0 } = {};
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delete container .NaN ;`,
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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const name = 'name';
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delete container[name];`,
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errors: [{ messageId: 'dynamicDelete' }],
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},
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{
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code: `const container: { [i: string]: 0 } = {};
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const getName = () => 'aaa';
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delete container[getName()];`,
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errors: [{ messageId: 'dynamicDelete' }],
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},
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],
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});

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