# JavaScript isNaN() Function
## Definition and Usage
The isNaN() function determines whether a value is NaN (Not-a-Number).
In JavaScript, NaN is the only value that is not equal to itself.
You can use this function to determine whether an arithmetic result is a legal number.
---
## Browser Support
| Element | Chrome | IE | Firefox | Safari | Opera |
|---------|--------|-----|---------|--------|-------|
| isNaN() | Yes | Yes | Yes | Yes | Yes |
---
## Syntax
```javascript
isNaN(value)
```
## Parameters
| Parameter | Description |
|-----------|-------------|
| value | Required. The value to be tested. |
## Return Value
| Type | Description |
|------|-------------|
| Boolean | Returns true if the value is NaN, otherwise returns false. |
## Technical Details
| Technical | Description |
|-----------|-------------|
| JavaScript Version: | 1.2 |
---
## More Examples
### Example 1
```html
Please input a value:
function myFunction() {
var x = document.getElementById("demo").value;
if (isNaN(x)) {
document.getElementById("pid").innerHTML = "Input is not a number";
} else {
document.getElementById("pid").innerHTML = "Input is a number";
}
}
```
### Example 2
```javascript
document.write(isNaN(123) + " ");
document.write(isNaN(-1.23) + " ");
document.write(isNaN(5-2) + " ");
document.write(isNaN(0) + " ");
document.write(isNaN("Hello") + " ");
document.write(isNaN("2005/12/12") + " ");
```
Output:
```
false
false
false
false
true
true
```
---
## Related Pages
JavaScript Reference: (
---
YouTip