Add Two Textbox Values And Display The Sum In A Third Textbox Automatically

I have assigned a task to add two textbox values.I want the result of addition to appear in the 3rd textbox,as soon as enter the values in the first two textboxes,without pressing

Solution 1:

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;
       }
   }

Solution 2:

Try this: Open given fiddle in CHROME

function sum() {
      var txtFirstNumberValue = document.getElementById('txt1').value;
      var txtSecondNumberValue = document.getElementById('txt2').value;
      var result = parseInt(txtFirstNumberValue) + parseInt(txtSecondNumberValue);
      if (!isNaN(result)) {
         document.getElementById('txt3').value = result;
      }
}

HTML

<input type="text" id="txt1"  onkeyup="sum();" />
<input type="text" id="txt2"  onkeyup="sum();" />
<input type="text" id="txt3" />

DEMO HERE

Solution 3:

i didn't find who made elegant answer , that's why let me say :

Array.from(
   document.querySelectorAll('#txt1,#txt2')
).map(e => parseInt(e.value) || 0) // to avoid NaN
.reduce((a, b) => a+b, 0)

window.sum= () => 
 document.getElementById('result').innerHTML=    
   Array.from(
     document.querySelectorAll('#txt1,#txt2')
   ).map(e=>parseInt(e.value)||0)
   .reduce((a,b)=>a+b,0)

<input type="text" id="txt1" onkeyup="sum()"/>
<input type="text" id="txt2" onkeyup="sum()"  style="margin-right:10px;"/><span id="result"></span>

Solution 4:

Well, base on your code, you would put onkeyup=sum() in each text box txt1 and txt2

Solution 5:

well I think the problem solved this below code works:

function sum() {
    var result=0;
       var txtFirstNumberValue = document.getElementById('txt1').value;
       var txtSecondNumberValue = document.getElementById('txt2').value;
    if (txtFirstNumberValue !="" && txtSecondNumberValue ==""){
        result = parseInt(txtFirstNumberValue);
    }else if(txtFirstNumberValue == "" && txtSecondNumberValue != ""){
        result= parseInt(txtSecondNumberValue);
    }else if (txtSecondNumberValue != "" && txtFirstNumberValue != ""){
        result = parseInt(txtFirstNumberValue) + parseInt(txtSecondNumberValue);
    }
       if (!isNaN(result)) {
           document.getElementById('txt3').value = result;
       }
   }