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isIn()

isIn<T>(array): (value) => boolean

Creates a predicate function that determines if a value exists in a given array.

Type Parameters​

T​

T

The type of the array elements and value

Parameters​

array​

T[]

The array to search within

Returns​

(value): boolean

Parameters​

value​

T

Returns​

boolean

Remarks​

  • Pure function with no side effects
  • Uses Array.prototype.includes() for membership testing
  • Uses strict equality (===) for element comparison
  • Works with any type that can be compared with strict equality
  • Useful for array filtering and validation predicates

Example​

const isValidStatus = isIn(['pending', 'approved', 'rejected']);
isValidStatus('pending');  // true
isValidStatus('unknown');  // false

const isPrime = isIn([2, 3, 5, 7, 11, 13]);
isPrime(7);  // true
isPrime(10); // false

// Useful with arrays
const userIds = [101, 102, 103, 104];
const activeUsers = [101, 103, 105, 106];
const validActiveUsers = activeUsers.filter(isIn(userIds)); // [101, 103]