coding_problem.js

function sameChars(str1, str2) {
  let str1Arr = str1.split('');
  let str2Arr = str2.split('');
  for (let index = 0; index < str2Arr.length; index += 1) {
    let char = str2Arr[index];
    if (!str1.includes(char)) return false;
  }
  return true;
}

function isMerge(string, part1, part2) {
  let stringArr = string.split('');
  let part1Arr = part1.split('');
  let part2Arr = part2.split('');
  let placeInString = 0;

  let regexstring = `[${string}]`
  let regex = new RegExp(regexstring, 'gi');
  if (sameChars(string, part1) === false || sameChars(string, part2) === false) return false;
  if ((part1.length + part2.length) !== string.length) return false;

  for (let index = 0; index < part1Arr.length; index += 1) {
    let char = part1Arr[index];
    let charIndexInString = stringArr.indexOf(char);
    if (charIndexInString >= placeInString) {
      stringArr.splice(charIndexInString, 1);
      placeInString = charIndexInString;
    } else {
      return false;
    }

  }
  placeInString = 0;

  for (let index = 0; index < part2Arr.length; index += 1) {
    let char = part2Arr[index];
    let charIndexInString = stringArr.indexOf(char);
    if (charIndexInString >= placeInString) {
      stringArr.splice(charIndexInString, 1);
      placeInString = charIndexInString;
    } else {
      return false;
    }
  }

  if (stringArr.length !== 0) return false;
  return true;
}

console.log(isMerge('codewars', 'code', 'wars')); // true
console.log(isMerge('codewars', 'cdw', 'oears')); // true
console.log(isMerge('codewars', 'oears', 'cdw')); // true
console.log(isMerge('codewars', 'cod', 'wars')); // false
console.log(isMerge('codewars', 'cod', 'war%')); // false
console.log(isMerge('codewars', 'co3', 'wars')); // false
console.log(isMerge('codewars', 'dcw', 'oears')); // false
console.log(isMerge('codewars', 'cdw', 'eoars')); // false
console.log(isMerge('codewars', 'cod', 'ewars')); // true
console.log(isMerge('codewars', 'coe', 'dwars')); // true
console.log(isMerge('codewars', 'codd', 'ewars')); // true