Creates a keyed JS object from an array, given a function to produce the keys and a function to produce the values from each item in the array.

const phoneBook = [
  { name: 'Jon', num: '555-1234' },
  { name: 'Jenny', num: '867-5309' }
]

// { Jon: '555-1234', Jenny: '867-5309' }
const phonesByName = keyValMap(
  phoneBook,
  entry => entry.name,
  entry => entry.num
)