How do I make this function a number? [duplicate]

I’m learning JavaScript and I wanted to accept user input and add a number to it ,but instead of outputting 12+12 = 24 it’s outputting 12+ 12 = 1212.

document.getElementById("mybutton").onclick = function(){
  var myAge = document.getElementById("mytext").value + 12;
  document.getElementById("value").innerHTML = myAge;
}

I tried doing:
myName = Number(myName)
but it didn’t work