82 lines
2.2 KiB
Plaintext
82 lines
2.2 KiB
Plaintext
---
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description: 'Enforce `includes` method over `indexOf` method.'
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---
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import Tabs from '@theme/Tabs';
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import TabItem from '@theme/TabItem';
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> 🛑 This file is source code, not the primary documentation location! 🛑
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>
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> See **https://typescript-eslint.io/rules/prefer-includes** for documentation.
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Prior to ES2015, `Array#indexOf` and `String#indexOf` comparisons against `-1` were the standard ways to check whether a value exists in an array or string, respectively.
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Alternatives that are easier to read and write now exist: ES2015 added `String#includes` and ES2016 added `Array#includes`.
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This rule reports when an `.indexOf` call can be replaced with an `.includes`.
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Additionally, this rule reports the tests of simple regular expressions in favor of `String#includes`.
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> This rule will report on any receiver object of an `indexOf` method call that has an `includes` method where the two methods have the same parameters.
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> Matching types include: `String`, `Array`, `ReadonlyArray`, and typed arrays.
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## Examples
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<Tabs>
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<TabItem value="❌ Incorrect">
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```ts
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const str: string;
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const array: any[];
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const readonlyArray: ReadonlyArray<any>;
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const typedArray: UInt8Array;
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const maybe: string;
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const userDefined: {
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indexOf(x: any): number;
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includes(x: any): boolean;
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};
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str.indexOf(value) !== -1;
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array.indexOf(value) !== -1;
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readonlyArray.indexOf(value) === -1;
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typedArray.indexOf(value) > -1;
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maybe?.indexOf('') !== -1;
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userDefined.indexOf(value) >= 0;
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/example/.test(str);
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```
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</TabItem>
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<TabItem value="✅ Correct">
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```ts
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const str: string;
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const array: any[];
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const readonlyArray: ReadonlyArray<any>;
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const typedArray: UInt8Array;
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const maybe: string;
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const userDefined: {
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indexOf(x: any): number;
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includes(x: any): boolean;
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};
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str.includes(value);
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array.includes(value);
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!readonlyArray.includes(value);
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typedArray.includes(value);
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maybe?.includes('');
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userDefined.includes(value);
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str.includes('example');
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// The two methods have different parameters.
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declare const mismatchExample: {
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indexOf(x: unknown, fromIndex?: number): number;
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includes(x: unknown): boolean;
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};
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mismatchExample.indexOf(value) >= 0;
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```
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</TabItem>
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</Tabs>
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{/* Intentionally Omitted: When Not To Use It */}
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