fix_parens.js

function strip(str) {
  let start = 0;
  let end = str.length - 1;
  let startCache = '';
  let endCache = '';
  while (str[start] != '(') {
    if (str[start] != ')') {
      startCache += str[start];
    }
    ++start;
  }
  while (str[end] != ')') {
    if (str[end] != '(') {
      endCache += str[end];
    }
    --end;
  }
  return startCache + str.substring(start, end + 1) + endCache;
}