Question: Basically I have the following code:

```
<input type="text" value="123" id="txtbox">
<script>
var myVar = document.getElementById('txtbox').value;

if (myVar.substring) {
alert('string');
} else{
alert('number');
}
</script>

```

No matter what value you put in the textbox, it will always alert `string`. Is there a way that if you put a number in the textbox it will alert `number` instead of string? Thank you.

Answer: 
`value` on `input` elements is **always** a string. It might be a string of digits.

If you want to know whether that string only contains valid numbers, you have to parse it (and decide what you consider a valid number, and allow for that).

For instance, you'll get people telling you to use `parseInt(myVar)` or the unary `+` (`+myVar`) or `isNaN(myVar)` (which does what the unary `+` does) or `Number(myVar)` (same), **but**:

1. `parseInt` only parses the beginning of the string, `parseInt("345foo")` is `345`
2. `parseInt` is, of course, only for whole numbers; you'd want `parseFloat` for numbers with fractional portions
3. All of those will fail to understand thousands separators
4. All of those will fail to understand a decimal separator that isn't `.` (e.g., in many locales it's `,` or sometimes even a space)
5. `+myVar` and `Number(myVar)` and `isNaN(myVar)` and such will treat an empty string as `0`

...that kind of thing. So you have to do some prep on the string according to what input you want to accept.

Once you've decide what format(s) to handle, there are a dozen questions with answers here about doing the actual parsing:

* [*How do I Convert a String into an Integer in JavaScript?*](https://stackoverflow.com/questions/1133770/how-do-i-convert-a-string-into-an-integer-in-javascript) (note that's integer-specific)
* [*What's the fastest way to convert String to Number in JavaScript?*](https://stackoverflow.com/questions/12862624/whats-the-fastest-way-to-convert-string-to-number-in-javascript)
is `isNaN` (literally "is Not a Number"):

```
var myVar = document.getElementById('txtbox').value;

var myNum = +myVar;//as suggested by T.J. 
if (isNaN(myNum)) {
   alert('string');
} else{
   alert('number');
}

```