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JavaScript isNaN() Function
JavaScript Global Functions
Definition and Usage
The isNaN() function determines whether a value is an illegal number (Not-a-Number).
This function returns true if the value is NaN, and false if not.
Syntax
isNaN(value)
| Parameter | Description |
|---|---|
| value | Required. The value to be tested |
Browser Support
The isNaN() function is supported in all major browsers.
Example
Example
Check whether a number is an illegal number:
<script>
document.write(isNaN(123)+ "<br>");
document.write(isNaN(-1.23)+ "<br>");
document.write(isNaN(5-2)+ "<br>");
document.write(isNaN(0)+ "<br>");
document.write(isNaN("Hello")+ "<br>");
document.write(isNaN("2005/12/12")+ "<br>");
</script>
document.write(isNaN(123)+ "<br>");
document.write(isNaN(-1.23)+ "<br>");
document.write(isNaN(5-2)+ "<br>");
document.write(isNaN(0)+ "<br>");
document.write(isNaN("Hello")+ "<br>");
document.write(isNaN("2005/12/12")+ "<br>");
</script>
The output of the code above will be:
false
false
false
false
true
true
false
false
false
true
true
Try it yourself »
JavaScript Global Functions
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