# Number validation in javascript example

Learn javascript number function to check input is a number, how to check range, eval function, check number validation in javascript example.

In JavaScript there is only one type for all numbers, all numbers are treated as floating-point numbers. though the dot is not displayed if there is no digit after the decimal point.

Converting object to Number

JavaScript has in-built Number function to convert any object to number, Let's take a look at some examples of how to convert different object values to numbers using `Number()` function in JavaScript.

```<script>
var a1 = new Date();
var a2 = true;
var a3 = false;
var a4 = 99.99;
var a5 = "999";
var a6 = "999 888";

document.write(Number(a1));

document.write(Number(a2));

document.writeln(Number(a3));

document.writeln(Number(a4));

document.writeln(Number(a5));

document.writeln(Number(a6));
</script>
```

After executing the above code here is the result!

use eval function to check number in JavaScript

Now think of a situation where you receive user input as number and do some calculation based on that. Suppose you receive a number as string, but you need to perform some calculation, in such scenario you have to use `eval()` function.

`eval()` is used for evaluating the expression for number validation in javascript.

```<script>
var n1 = 10;
var n2 = 5;
var stringFormat = n1 + " + " + n2;
document.writeln(stringFormat); // 10 + 5
// using eval method
document.writeln(eval(stringFormat)); // 15
</script>
```
Number to String in JavaScript

There is built-in `toString()` method in javscript to convert a integer value to a string.

```            var x = 721;
x.toString();            // returns 721 from variable x
(123).toString();        // returns 721 from literal 123
(700 + 21).toString();   // returns 721 from expression 700 + 21
```
Check input is number in JavaScript

You can check input is number in JavaScript using `isNaN` function this is a built-in function, simply check if input is a number.

```var inputV1="Your Age?";

if(isNaN(inputV1))
else
console.log("You are "+ inputV1);
```
Check number range in javascript

If you want to check if any number is within specified range using JavaScript, there is no built-in function to check range, but you can create a function like example below, here we have three parameters to the function, input value, minimum value and maximum limit.

```function isInRange(input, min, max) {
return ((input-min)*(input-max) <= 0);
}

console.log(isInRange(4, 1, 10));     // true
console.log(isInRange(-2, 1, 10));    // false
console.log(isInRange(11, 1, 10));    // false
```

The above JavaScript function to check number range- is a custom function, you can give any name; also can change the internal logic if you find more efficient way to do it.

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