What is the use of isNaN function?

The isNaN() function in JavaScript is used to determine whether a given value is NaN (Not-a-Number) or not. NaN is a special value that represents the result of an operation that is not a number, such as dividing by zero or taking the square root of a negative number.

The isNaN() function takes a single argument, which can be of any data type. If the argument is not a number (i.e., it is a string, object, or any other non-numeric data type), the function will attempt to convert it to a number. If the argument cannot be converted to a number, the function will return true. If the argument is a number (including the special values NaN, Infinity, and -Infinity), the function will return false.

Here's an example

sNote that the isNaN() function is not the same as the Number.isNaN() method, which was introduced in ECMAScript 6. The Number.isNaN() method is a stricter version of the isNaN() function that only returns true if the argument is the special value NaN, and returns false for any other value.