old_contents: var milkcocoa = new MilkCocoa("https://io-dhxa654wp.mlkcca.com/");
  var chatDataStore = milkcocoa.dataStore("chat");
  var textArea, board;
  window.onload = function(){
    textArea = document.getElementById("msg");
    board = document.getElementById("board");
  }
  
  function clickEvent(){
      var text = textArea.value;
      sendText(text);
      textArea.value = "";
  }
  
  function sendText(text){
    chatDataStore.push({message : text},function(data){
      console.log("送信完了!");
    });
  }
  
  chatDataStore.on("push",function(data){
    addText(data.value.message);
  });
  
  function addText(text){
    var msgDom = document.createElement("li");
    msgDom.innerText = text;
    board.appendChild(msgDom);
  }
new_contents: var milkcocoa = new MilkCocoa("https://io-dhxa654wp.mlkcca.com/");
  var chatDataStore = milkcocoa.dataStore("chat");
  var textArea, board;
  window.onload = function(){
    textArea = document.getElementById("msg");
    board = document.getElementById("board");
  }
  
  function clickEvent(){
    var text = textArea.value;
    sendText(text);
  }
  
  function sendText(text){
    chatDataStore.push({message : text},function(data){
      console.log("送信完了!");
      textArea.value = "";
    });
  }
  
  chatDataStore.on("push",function(data){
    addText(data.value.message);
  });
  
  function addText(text){
    var msgDom = document.createElement("li");
    msgDom.innerHTML = text;
    board.appendChild(msgDom);
  }
subject: change innerText into innerHTML