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92 lines
2.3 KiB
Text
92 lines
2.3 KiB
Text
---
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description: 'Enforce `includes` method over `indexOf` method.'
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---
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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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Until ES5, we were using `String#indexOf` method to check whether a string contains an arbitrary substring or not.
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Until ES2015, we were using `Array#indexOf` method to check whether an array contains an arbitrary value or not.
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ES2015 has added `String#includes` and ES2016 has added `Array#includes`.
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It makes code more understandable if we use those `includes` methods for the purpose.
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## Rule Details
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This rule is aimed at suggesting `includes` method if `indexOf` method was used to check whether an object contains an arbitrary value or not.
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If the receiver object of the `indexOf` method call has `includes` method and the two methods have the same parameters, this rule does suggestion.
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There are such types: `String`, `Array`, `ReadonlyArray`, and typed arrays.
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Additionally, this rule reports the tests of simple regular expressions in favor of `String#includes`.
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Examples of code for this rule:
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<!--tabs-->
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### ❌ Incorrect
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```ts
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let str: string;
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let array: any[];
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let readonlyArray: ReadonlyArray<any>;
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let typedArray: UInt8Array;
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let maybe: string;
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let 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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// simple RegExp test
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/foo/.test(str);
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```
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### ✅ Correct
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```ts
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let array: any[];
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let readonlyArray: ReadonlyArray<any>;
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let typedArray: UInt8Array;
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let 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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let mismatchExample: {
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indexOf(x: any, fromIndex?: number): 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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userDefined.includes(value);
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// the two methods have different parameters.
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mismatchExample.indexOf(value) >= 0;
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```
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## Options
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```jsonc
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// .eslintrc.json
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{
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"rules": {
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"@typescript-eslint/prefer-includes": "warn"
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}
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}
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```
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This rule is not configurable.
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## When Not To Use It
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If you don't want to suggest `includes`, you can safely turn this rule off.
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