age_range.js

const ageRange = birthYear => {
  // get age
  let age = new Date().getFullYear() - birthYear

  // range of ages
  const range = [
    0,
    4,
    9,
    14,
    17,
    24,
    29,
    34,
    39,
    44,
    49,
    54,
    59,
    64,
    69,
    74,
    79,
    84
  ]

  // find the closest
  let closest = range
  .reduce(function(prev, curr) {
    return (Math.abs(curr - age) < Math.abs(prev - age) ? curr: prev);
  });

  // find the index of the closest
  let idx = range.indexOf(closest)

  // start building result
  let result = ['Age', closest+1]

  // add to n or and over for over 85yo
  if (range[idx+1]) {
    result.push('to')
    result.push(range[idx+1])
  } else {
    result.push('and over')
  }

  // join it all together now...🍻
  return result.join(' ')
}

'Age 40 to 44'
console.log(ageRange(1979))

'Age 85 and over'
console.log(ageRange(1900))