问在div中的特定点追加字符串

EN

var words = ['dog'];
var output = "";
var gRand = "";
var gWordAry = "";

function startGame() {
  var rand = words[Math.floor(Math.random() * words.length)]; //gets a random word from the array, stores as rand
  var wordAry = rand.split(''); //splits random word into its own array and each letter is in the array
  gRand = rand; //stores random word as global var
  gWordAry = wordAry;
  alert(wordAry);
  $('#hangmanGame').show();
  $('#startBtn').hide();
  //alert(rand);
  for (i = 0; i < wordAry.length; i++) { //draws a dash for every letter in the random word array after split
    //draw canvas dash
    output += ' _ ';
    $('#wordGuess').html(output);
  }


  //alert(output);


}
currentIndex = 0
function guess(letter) {
  var letterID = letter.toLowerCase(); //converts letter to lowercase from html
  //alert(letterID);
  var foundLetter = 0;
  for (i = 0; i < gWordAry.length; i++) {
    if (gWordAry[i] == letterID && gWordAry[i] !== '_') { //if a letter in the word array = the letter clicked this will run
      //alert('correct');
      if (currentIndex == i){
      foundLetter++;
      gWordAry[i] = '_'
      displayLetter(letterID, currentIndex++);
        
      break;
        }
    }
  }
  if (foundLetter == 0) { //if no letters in the array are found this will run
    alert('Try Again');
  }

}
String.prototype.replaceAt = function(index, character) {
  return this.substr(0, index) + character + this.substr(index + character.length);
}

function displayLetter(letterID,i) {
  //displays all letters in the word
  var toReplace = $('#wordGuess').html();


 $('#wordGuess').html($('#wordGuess').html().replaceAt($('#wordGuess').html().indexOf('_'), letterID))
}
startGame()

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="hangmanGame">
  <div id="wordGuess"></div>
  <table style="margin: auto;position: relative;top: 10px;">
    <tr>
      <td>
        <button class="alphabet" type="button"></button>
      </td>
      <td>
        <button type="button" onclick="guess('A')" id="1" class="alphabet">A</button>
      </td>
      <td>
        <button type="button" onclick="guess('B')" id="2" class="alphabet">B</button>
      </td>
      <td>
        <button type="button" onclick="guess('C')" id="3" class="alphabet">C</button>
      </td>
      <td>
        <button type="button" onclick="guess('D')" id="4" class="alphabet">D</button>
      </td>
      <td>
        <button type="button" onclick="guess('E')" id="5" class="alphabet">E</button>
      </td>
      <td>
        <button type="button" onclick="guess('F')" id="6" class="alphabet">F</button>
      </td>
      <td>
        <button type="button" onclick="guess('G')" id="7" class="alphabet">G</button>
      </td>
      <td>
        <button type="button" onclick="guess('H')" id="8" class="alphabet">H</button>
      </td>
      <td>
        <button class="alphabet" type="button"></button>
      </td>
    </tr>
    <tr>
      <td>
        <button class="alphabet" type="button"></button>
      </td>
      <td>
        <button type="button" onclick="guess('I')" id="9" class="alphabet">I</button>
      </td>
      <td>
        <button type="button" onclick="guess('J')" id="10" class="alphabet">J</button>
      </td>
      <td>
        <button type="button" onclick="guess('K')" id="11" class="alphabet">K</button>
      </td>
      <td>
        <button type="button" onclick="guess('L')" id="12" class="alphabet">L</button>
      </td>
      <td>
        <button type="button" onclick="guess('M')" id="13" class="alphabet">M</button>
      </td>
      <td>
        <button type="button" onclick="guess('N')" id="14" class="alphabet">N</button>
      </td>
      <td>
        <button type="button" onclick="guess('O')" id="15" class="alphabet">O</button>
      </td>
      <td>
        <button type="button" onclick="guess('P')" id="16" class="alphabet">P</button>
      </td>
      <td>
        <button class="alphabet" type="button"></button>
      </td>
    </tr>
    <tr>
      <td>
        <button type="button" onclick="guess('Q')" id="17" class="alphabet">Q</button>
      </td>
      <td>
        <button type="button" onclick="guess('R')" id="18" class="alphabet">R</button>
      </td>
      <td>
        <button type="button" onclick="guess('S')" id="19" class="alphabet">S</button>
      </td>
      <td>
        <button type="button" onclick="guess('T')" id="20" class="alphabet">T</button>
      </td>
      <td>
        <button type="button" onclick="guess('U')" id="21" class="alphabet">U</button>
      </td>
      <td>
        <button type="button" onclick="guess('V')" id="22" class="alphabet">V</button>
      </td>
      <td>
        <button type="button" onclick="guess('W')" id="23" class="alphabet">W</button>
      </td>
      <td>
        <button type="button" onclick="guess('X')" id="24" class="alphabet">X</button>
      </td>
      <td>
        <button type="button" onclick="guess('Y')" id="25" class="alphabet">Y</button>
      </td>
      <td>
        <button type="button" onclick="guess('Z')" id="26" class="alphabet">Z</button>
      </td>
    </tr>
  </table>
</div>

for (i = 0; i < wordAry.length; i++) { //draws a dash for every letter in the random word array after split
    //draw canvas dash
    output += "<span id='letter" + i + "'>_</span>";
}
$('#wordGuess').html(output);

for (i = 0; i < gWordAry.length; i++) {
    if (gWordAry[i] === letterID) { //if a letter in the word array = the letter clicked this will run
        foundLetter++;
        displayLetter(letterID, i);
    }
}

function displayLetter(letterID, index) {
    //displays all letters in the word
    $('#letter' + index).text(letterID);
}