This package can perform some operations on strings and arrays:

findElementIndex takes an array and a predicate function and return the index of the first array element for which the function returns true

const array = ['max', 'ksysha', 'john'];
const isKsysha = person => person === 'ksysha'; 

findIndex(array, isKsysha) // -> 1

reverseString takes a string and returns a reversed string

const name = 'ksy';
const reversedName = reverseString(name); 

reversedName // -> 'ysk'