to alert user if user enters other than a valid number value in each text fields and to alert user enter number if any textfield is left blank

Question

<!DOCTYPE html>
<html>
<body bgcolor = "eeeeee">

<p> Add Section </p>

<label>Fir No :</label>

<input id="txt1"  type="text"/></br></br>

<label>Sec No :</label> 

<input id="txt2"  type="text"/></br></br>

<input type="button" name="Add" value="Add" onclick="addTwoNumber()"/>
<p id="demo"></p>
<script>
function myFunction() {
document.getElementById("demo").innerHTML = Date();
}
<!-- addition of two numbers-->

function addTwoNumber(){
var a = document.getElementById("txt1").value;
var b = document.getElementById("txt2").value;

var x = Number(a) + Number(b);
document.getElementById("demo").innerHTML = "Add Value: " + x;
}
</script>

</body>
</html>

i have written a code in this code i am not able to alert user if he enters other than number and also how to alert the user if he left blank without filling value in addition

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN — epascarello, Dec 31 '14 at 05:10

Saravana Kumar · Answer 1 · 2014-12-31T05:30:51.103

Use the isNaN() to check for valid number.

function addTwoNumber(){
var a = document.getElementById("txt1").value;
var b = document.getElementById("txt2").value;

if(a == "")
{
    alert("enter txt1 value");
    return;
}    

if(b == ""){
    alert("enter txt2 value");
    return;}

if(isNaN(a)){
    alert("enter valid number txt1 value");
    return;}


if(isNaN(b)){
    alert("enter valid number txt2 value");
    return;}

var x = Number(a) + Number(b);
document.getElementById("demo").innerHTML = "Add Value: " + x;
}

score 0 · Accepted Answer · answered Dec 31 '14 at 05:21

Try below code:

 <!DOCTYPE html>
 <html>
 <body bgcolor = "eeeeee">
 <p> Add Section </p>
 <label>Fir No :</label>
 <input id="txt1"  type="text"/></br></br>
 <label>Sec No :</label>
 <input id="txt2"  type="text"/></br></br>
 <input type="button" name="Add" value="Add" onclick="addTwoNumber()"/>
 <p id="demo"></p>
 <script>
 function myFunction() {
 document.getElementById("demo").innerHTML = Date();
 }
 <!-- addition of two numbers-->

 function addTwoNumber(){
 var a = document.getElementById("txt1").value;
 var b = document.getElementById("txt2").value;
 if (a == "" || b == "")
 {
    alert('Please enter any number');
    return;
 }
 if (isNaN(a) || isNaN(b))
 {
    alert('Please enter any number');
    return;
 }
 var x = Number(a) + Number(b);
 document.getElementById("demo").innerHTML = "Add Value: " + x;
 }
 </script>

 </body>
 </html>

to alert user if user enters other than a valid number value in each text fields and to alert user enter number if any textfield is left blank

2 Answers2