I build a Scoreboard

what it does when someone click the +500 button it will add 500 to the value in the score board i.e it will add 500 to the value of p tag

   <div class=box> 

 <h2>Teams</h2>

 <div class=score>

    <p id=p1 class=lead>230</p>

  </div>

  /div>

 <button id=b1>+500</button>

JavaScript for it

var myScore = document.getElementById(b1);

myScore.onclick = function () {

    var newScore = document.getElementById(p1).innerHTML;

    var value = newScore + 500;

    document.getElementById(p1).innerHTML = value;

};

but this is showing me 230500 instead of 730. how to change my inner html value 230 in integer form ??