Using NaN value in JavaScript _ basic knowledge

This article mainly introduces how to use the NaN value in JavaScript, which is the basic knowledge in JS learning, A friend may refer to the literal constant NaN without quotation marks as a special value, indicating that it is not a non-number. Since NaN is always a case of unequal comparison, taking any number, including NaN, is usually an error condition used to indicate that a function with a valid number should be returned.

Note: Use the isNaN () global function to check whether the value is NaN.
Syntax

You can use the following syntax to access properties:

Var val = Number. NaN;

Example:

Here, dayOfMonth is allocated with NaN. if it is greater than 31 and a message is displayed, the valid range is: