block12.js

let arr = [10, 2, 4]
// product
arr.reduce((a, b) => a * b) // 80

arr = [false, true, true]
// all
arr.reduce((a, b) => a && b) // false

// any
arr.reduce((a, b) => a || b) // true

// length (obviously, just use the length property instead in real code)
arr.reduce((a) => a + 1, 0) // 3

// reverse
arr.reduce((a, b) => [b, ...a], []) // [true, true, false]

// add a prefix to all the first child key names of an object
const addPrefix = (prefix, obj) =>
  Object.entries(obj).reduce((result, [key, val]) => {
    result[prefix + key] = val
    return result
  }, {})

// addPrefix usage
const myObj = { a: 1, b: 2 }
addPrefix('hidy-ho-errybody__', myObj)
// returns { hidy-ho-errybody__a: 1, hidy-ho-errybody__b: 2 }