<input type="text" id="num1" value="">
    <button>+</button>
    <input type="text" id="num2" value="">
    <button id="equal" onclick="myFunction()">=</button>
    <input type="text" id="result">

var num1= document.getElementById("num1").value;
    var num2= document.getElementById("num2").value;
    var x= parseInt('num1')+ parseInt('num2');
    function myFunction(){
    document.getElementById("result").innerHTML=x;
    }