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JavaScript Math Functions

Checking number using isNaN function

JavaScript has one important function isNaN() to check any data is number or string. This function isNaN() is remembered as short form is Is Not a Number. This function returns true if the data is string and returns false if the data is a number. Here is one simple example to check one string. We will use one if else condition check to display a message accordingly. Here is the code.
var my_string="This is a string";
document.write ("this is not a number ");
}else{document.write ("this is  a number ");
We will integrate this function to one JavaScript prompt. Here we will ask the user to enter a number. The value entered by user we will check by isNan function and display message accordingly.

Demo of isNan

Here is the code.
var my_string = prompt("Please enter a number","");
document.write ("this is not a number ");
}else{document.write ("this is  a number ");

Number of User Comments : 8


yes, agree,
this is very useful topic it helps me in project,
good concept not finding in other sites
Dhaval Shingala25-02-2010
The simplest Way is Why u check entered input is Number or not

just check on Keypress Event is number or not

The Function for checking Is number is

function isNumberKey(B,C){if(!C){C=0}var A=(B.which)?B.which:event.keyCode;if(A>31
Rakesh Joshi16-04-2010
I observed that isNaN has a flaw. If we enter a value with alphabets at the start, it will detect. But if it starts with a number and continues with alphabets or ends with alphabets, then isNaN will return false, meaning to say it is a number, which is not the desired output. Is there any other alternative?
write a javascript code that will pop-up when an input of not a number is enter and return true when number data is enter. but without using in inbuild function such as isNan.
This is okay..
Use Integer.parseInt("value") instead and put that in a try catch block.
@Ray, this is JavaScript not Java.
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