arrayToObjectUsingReduce

reduce.js

let string = "aabbbcbck"
let strArr = string.split("") // [ 'a', 'a', 'b', 'b', 'b', 'c', 'b', 'c', 'k' ]

// Array to object using reduce - counting each letter occurances
let obj = strArr.reduce((acc,ltr) => {
    acc[ltr] = ++acc[ltr] || 1
    return acc
  },{})
console.log("reduce - object: ", obj) // { a: 2, b: 4, c: 2, k: 1 }