old_contents: /* function to convert n-dimension array into 1-D array */
  module.exports = function flatten(arr, tarr) {
      for (let i of arr) {
          if (Array.isArray(i)) {
              flatten(i, tarr);
          }
          else {
              tarr.push(i);
          }
      }
  }
new_contents: /* function to convert n-dimension array into 1-D array  */
  module.exports = function flatten(arr, tarr) {
      for (let i of arr) {
          if (Array.isArray(i)) {
              flatten(i, tarr);
          }
          else {
              tarr.push(i);
          }
      }
  }
  
subject: Update flatten.js