Strip double AA/BB/CC's repeatedly

interview.js

// this is basically what I submitted, and it worked with the given examples
function(S) {
  const A = S.split('')
  
  for (let i = 0; i < A.length; i++) {
    // skip till you find a double digit
    if (A[i] !== A[i+1]) continue
    
    // find the palindrome
    let start = i, end = i + 1
    while (start >= 0 && end < A.length && A[start] === A[end]) {
      start--
      end++
    }
    
    // I could've simply deleted elements on the loop above, but isn't it the same anyway?
    for (let j = start + 1; j < end - 1; j++) A[j] = undefined
    
    // skip to AFTER the palindrome search so you don't have to do this work again.
    // Therefore, no element is searched twice! So it's O(n)
    i = end
  }
  
  return A.filter(e => e).join('')
}