Add Two Numbers and Display Result in Textbox With JavaScript

Add two numbers and display result in textbox with Javascript

Here a working fiddle: http://jsfiddle.net/sjh36otu/

        function add_number() {

            var first_number = parseInt(document.getElementById("Text1").value);
            var second_number = parseInt(document.getElementById("Text2").value);
            var result = first_number + second_number;

            document.getElementById("txtresult").value = result;
        }

Add Two numbers from textbox using JavaScript

You can simply do it like this

<input type="text" id="num1"><br><br>
<input type="text" id="num2"><br><br>
<button id="add">Answer</button><br>
<p id="para"></p>
<script>
    let add=document.getElementById("add");
    add.addEventListener("click",function(){
       var num1 = document.getElementById('num1').value;
       var num2 = document.getElementById('num2').value;
       var res = parseInt(num1) + parseInt(num2);
       document.getElementById("para").innerHTML = res ;
    });
</script>

here is the demo of working code

let add=document.getElementById("add");

add.addEventListener("click",function(){
  var num1 = document.getElementById('num1').value;
  var num2 = document.getElementById('num2').value;
  var res = parseInt(num1) + parseInt(num2);
  document.getElementById("para").innerHTML = res ;
});

<input type="text" id="num1"><br><br>
<input type="text" id="num2"><br><br>
<button id="add">Answer</button>
<br>
<p id="para"></p>

Add two textbox values and display the sum in a third textbox automatically

try this

  function sum() {
       var txtFirstNumberValue = document.getElementById('txt1').value;
       var txtSecondNumberValue = document.getElementById('txt2').value;
       if (txtFirstNumberValue == "")
           txtFirstNumberValue = 0;
       if (txtSecondNumberValue == "")
           txtSecondNumberValue = 0;

       var result = parseInt(txtFirstNumberValue) + parseInt(txtSecondNumberValue);
       if (!isNaN(result)) {
           document.getElementById('txt3').value = result;
       }
   }

Add three numbers and display result in textbox with Javascript

Two issues:

(1) Small typo in your last line, you used getElementByID instead of getElementById

(2) You need to account for the case where there is no value, one way to do this is to or it with 0 (which evaluates to 0 if there is no value).

Here is a working example:

function sum()
{
  var w = document.getElementById('num1').value || 0;
  var x = document.getElementById('num2').value || 0;
  var y = document.getElementById('num3').value || 0;

  var z=parseInt(w)+parseInt(x)+parseInt(y);

  document.getElementById('final').value=z;
};

https://jsfiddle.net/yq60qad0/

How to Add Two Input Values And Show In The Third Input Box ?? with simple JavaScript like this help me where i was wrong

You should have the attribute id for the controls which you are referencing in your code with getElementById(). You also have to convert the string value to number to perform the arithmetic operation:

function sum(){  var val1 = document.getElementById('val1').value;  var val2 = document.getElementById('val2').value;  var sum = Number(val1) + Number(val2);  document.getElementById('total').value = sum;}

<input type="text" name="val1" id="val1"><br><br><input type="text" name="val2" id="val2"><br><br><input name="total" id="total" value=""><br><br><button type="button" onclick="sum()" name="btn">Add</button>

Add Two Numbers and Display Result in Textbox With JavaScript