Check if all items in an array are equal

JavaScript version

const areEqual = (arr) => arr.length > 0 && arr.every((item) => item === arr[0]);

// Or
const areEqual = (arr) => new Set(arr).size === 1;

TypeScript version

const areEqual = <T,_>(arr: T[]): boolean => arr.length > 0 && arr.every((item) => item === arr[0]);

// Or
const areEqual = <T,_>(arr: T[]): boolean => new Set(arr).size === 1;

Examples

areEqual([1, 2, 3, 4]); // false
areEqual(['hello', 'hello', 'hello']); // true