findSmallestInterval.js

const findSmallestInterval = (numbers) => {
  numbers.sort((a, b) => a - b)
  
  let r = Number.MAX_SAFE_INTEGER
  
  numbers.forEach((e, i) => {
    if (i + 1 > numbers.length)
      return
    
    const d = Math.abs(e - numbers[i + 1])
    if (d < r)
        r = d
  })
  
  return r
}
// [1, 6, 4, 2, 8] => 1 (between 2 and 1)