solution.js

/**
 * @param {string} word1
 * @param {string} word2
 * @return {string}
 */
var mergeAlternately = function (word1, word2) {
  let str = "";

  word1 = word1.split(""), word2 = word2.split("");
  for (let i = 0; i < word1.length; i++) {
    str += word1[i];
    if (word2.length > 0) str += word2.shift();
  }

  str += word2.join("");

  return str;
};

// var mergeAlternately = function (word1, word2) {
//   let str = "";
//   word1 = word1.split(""), word2 = word2.split("");
//   while (word1.length > 0 || word2.length > 0) {
//     let curr1 = "", curr2 = "";
//     console.log(word1)
//     console.log(word2)
//     if (word1.length > 0) {
//       curr1 = word1.shift();
//     }
//
//     if (word2.length > 0) {
//       curr2 = word2.shift();
//     }
//
//     str += curr1 + curr2;
//   }
//
//   return str;
// };