How to identify input if its decimal in javascript

Question

I've created a code on where i can try out javascript's conditions and the code goes like this: the user enter's a decimal number and an alert box will say that it is a decimal number.If it is not a decimal number, an alert box will pop up and say that it is not a decimal number. However, the problem is I don't know what to put in my IF conditional statement to identify if its decimal.

Here is my code:

 var a = document.getElementById("txt1").value;

 if (a == ?){
    alert("It is a decimal number!");
 } else {
    alert("It is not a decimal number!");
 }

I hope someone can help me out. A total beginner. Thanks!

http://stackoverflow.com/questions/2304052/check-if-a-number-has-a-decimal-place-is-a-whole-number — sinisake, Mar 02 '14 at 11:31
`if (/^-?\d+(\.\d+)?$/.test(input))` this is might be good enough for you. also google never hurts. — gdoron, Mar 02 '14 at 11:33
I think a further definition of what you mean by `decimal` would help. Some examples of what would and would not be acceptable inputs from a user. Edit your question and you even earn a badge. — Xotic750, Mar 02 '14 at 11:47

score 1 · Answer 1 · answered Mar 02 '14 at 12:45

The elegant way is to use regular expression but sometimes regular expressions can frustrate novice programmers. Check this example. I hope it helps you.

var a = document.getElementById("txt1").value;

if (!isNaN(parseFloat(a)) && a.toString().indexOf(".") == -1){
    alert("It is a decimal number!");
} else {
    alert("It is not a decimal number!");
}

Best regards,

Sam · Answer 2 · 2018-06-03T07:10:59.840

0

Here's an example-

var a = prompt("Type in any number");

var b = parseInt(a);

if(a !== b) {
    alert("This is a decimal number!");
}
else {
    alert("This is an integer");
}

edited Jun 03 '18 at 07:10

answered Jun 02 '18 at 22:55

Sam

1
2

Chester Ayala · Answer 3 · 2021-05-18T19:28:09.530

0

Use RegEx.

var value = prompt('Enter decimal here senpai', '0.0');

if (/^\d*\.?\d*$/.test(value)) {
    console.log('I\'m a decimal. Nya~');
}

edited May 18 '21 at 19:28

answered May 18 '21 at 19:14

Chester Ayala

201
2
8

score -1 · Answer 4 · answered Sep 30 '14 at 05:44

     function decimal_only(e) {

         var charCode = (e.which) ? e.which : window.event.keyCode
         if (charCode != 46 && charCode > 31 && (charCode < 48 || charCode > 57)) {
             return false;
         }

         if (charCode == 46) { //Now Check The Decimal only allow 1 decimal
             if (e.value.indexOf('.') > -1) {
                 return false;
             }
         }
         return true;
     }

score -2 · Answer 5 · answered Mar 02 '14 at 11:34

-2

You can use a simple check

if(a != Math.floor(a))
{
  alert("It is a decimal number!");
} else {
        alert("It is not a decimal number!");
}

or

if(a - Math.floor(a) != 0) //then its with decimal
{
    alert("It is a decimal number!");
} else {
    alert("It is not a decimal number!");
}

answered Mar 02 '14 at 11:34

Saurabh Sharma

2,422
4
20
41

Since when is `"Hello World"` a decimal number? – Ingo Bürk Mar 02 '14 at 11:38
Consider a situation a user passes some number in the input – Saurabh Sharma Mar 02 '14 at 11:40
The question is how to intercept a user not typing a decimal number. `"Foo"` is not a decimal number, but your code won't intercept that. Hence it's wrong. – Ingo Bürk Mar 02 '14 at 11:42

How to identify input if its decimal in javascript

5 Answers5