code: function transferCase(source, target) {
    let cased = '';
  
    for (let i = 0, l = target.length; i < l; i++) {
      const c = source[i].toLowerCase() === source[i] ?
        'toLowerCase' :
        'toUpperCase';
  
      cased += target[i][c]();
    }
  
    return cased;
  }
docs: Function used to apply source word's case to target word.
  
  @param  {string} source - Source word.
  @param  {string} target - Target word.
  @return {string}