arrayIncludes

Reports using .indexOf() comparisons that can be replaced with .includes().

✅ This rule is included in the ts stylistic and stylisticStrict presets.

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. ES2015 added String.prototype.includes() and ES2016 added Array.prototype.includes(), which are more readable and expressive.

This rule reports when an .indexOf() comparison can be replaced with .includes(). It checks for any receiver object that has both .indexOf() and .includes() methods with compatible parameters.

Matching types include: String, Array, ReadonlyArray, and typed arrays.

declare const 
const array: number[]
array: number[];
declare const 
const value: number
value: number;
const array: number[]
array.
Array<number>.indexOf(searchElement: number, fromIndex?: number): number
Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
@param ― searchElement The value to locate in the array.
@param ― fromIndex The array index at which to begin the search. If fromIndex is omitted, the search starts at index 0.
indexOf(
const value: number
value) !== -1;

declare const 
const array: number[]
array: number[];
declare const 
const value: number
value: number;
const array: number[]
array.
Array<number>.indexOf(searchElement: number, fromIndex?: number): number
Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
@param ― searchElement The value to locate in the array.
@param ― fromIndex The array index at which to begin the search. If fromIndex is omitted, the search starts at index 0.
indexOf(
const value: number
value) === -1;

declare const 
const array: number[]
array: number[];
declare const 
const value: number
value: number;
const array: number[]
array.
Array<number>.indexOf(searchElement: number, fromIndex?: number): number
Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
@param ― searchElement The value to locate in the array.
@param ― fromIndex The array index at which to begin the search. If fromIndex is omitted, the search starts at index 0.
indexOf(
const value: number
value) > -1;

declare const 
const array: number[]
array: number[];
declare const 
const value: number
value: number;
const array: number[]
array.
Array<number>.indexOf(searchElement: number, fromIndex?: number): number
Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
@param ― searchElement The value to locate in the array.
@param ― fromIndex The array index at which to begin the search. If fromIndex is omitted, the search starts at index 0.
indexOf(
const value: number
value) >= 0;

declare const 
const str: string
str: string;
const str: string
str.
String.indexOf(searchString: string, position?: number): number
Returns the position of the first occurrence of a substring.
@param ― searchString The substring to search for in the string
@param ― position The index at which to begin searching the String object. If omitted, search starts at the beginning of the string.
indexOf("test") !== -1;

declare const 
const array: number[]
array: number[];
declare const 
const value: number
value: number;
const array: number[]
array.
Array<number>.includes(searchElement: number, fromIndex?: number): boolean
Determines whether an array includes a certain element, returning true or false as appropriate.
@param ― searchElement The element to search for.
@param ― fromIndex The position in this array at which to begin searching for searchElement.
includes(
const value: number
value);

declare const 
const array: number[]
array: number[];
declare const 
const value: number
value: number;
!
const array: number[]
array.
Array<number>.includes(searchElement: number, fromIndex?: number): boolean
Determines whether an array includes a certain element, returning true or false as appropriate.
@param ― searchElement The element to search for.
@param ― fromIndex The position in this array at which to begin searching for searchElement.
includes(
const value: number
value);

declare const 
const str: string
str: string;
const str: string
str.
String.includes(searchString: string, position?: number): boolean
Returns true if searchString appears as a substring of the result of converting this
object to a String, at one or more positions that are
greater than or equal to position; otherwise, returns false.
@param ― searchString search string
@param ― position If position is undefined, 0 is assumed, so as to search all of the String.
includes("test");

declare const 
const array: number[]
array: number[];
declare const 
const value: number
value: number;
const 
const index: number
index = 
const array: number[]
array.
Array<number>.indexOf(searchElement: number, fromIndex?: number): number
Returns the index of the first occurrence of a value in an array, or -1 if it is not present.
@param ― searchElement The value to locate in the array.
@param ― fromIndex The array index at which to begin the search. If fromIndex is omitted, the search starts at index 0.
indexOf(
const value: number
value);

Options

This rule is not configurable.

When Not To Use It

If you need to support environments that don’t have Array.prototype.includes() (pre-ES2016) or String.prototype.includes() (pre-ES2015), or if you need the actual index returned by .indexOf(), you may disable this rule.

Equivalents in Other Linters

ESLint: @typescript-eslint/prefer-includes
Oxlint: @typescript-eslint/prefer-includes

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arrayIncludes

Examples

Options

When Not To Use It

Further Reading

Equivalents in Other Linters