longestCommonPrefix.js

var longestCommonPrefix = function(strs) {
  const firstStr = strs[0];
  if (!firstStr) return '';

  let condition = true;
  let count = -1;
  while(condition) {
    count += 1;

    if (count === firstStr.length) {
      condition = false;
    } else {
      condition = strs.every(str => (
        firstStr[count] === str[count] 
      ));
    }

  }
  return firstStr.slice(0, count);
};