Check if all items in an array are equal

JavaScript

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

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

TypeScript

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