Avoiding falsy values in JavaScript arrays

tl;dr: use Array.filter(Boolean) to filter out falsy values and avoid errors.

// Fun function that converts a name into a
// 4 all-cap letters display name
const makeDisplayName = name => (
  name.charAt(0) + name.slice(1).replace(/a|e|i|o|u/g, "")
).toUpperCase().slice(0, 4);
const displayNames = [
  null, "orange", "apple", "mango", undefined…