Comparing the value to itself may be either a refactoring error or an outdated way of checking if the value is of a numeric data type but not a
valid number. This special numeric value is represented by NaN global property, where NaN stands for "Not-a-Number".
NaN is returned as a result when an arithmetic operation or mathematical function is performed, and the result is undefined or
unrepresentable as a valid number.
Detecting whether a value is NaN in JavaScript was previously problematic because of the way NaN behaves in comparison
operations. NaN is not equal to any value, including itself, so comparing the value to NaN will always return false. In
other words, if a value is not equal to itself, it can only be NaN.
This method of detecting NaN can be confusing and should be avoided. ES6 introduced a special function Number.isNaN()
which only returns true if the argument is NaN value. For clarity and consistency this function should be used to detect
NaN instead of all other methods.
if (value !== value){ // Noncompliant: use Number.isNaN()
processNaN(value);
}
To fix your code replace self-comparison with Number.isNaN() function.
if (Number.isNaN(value)){
processNaN(value);
}
Do not confuse Number.isNaN() with the legacy global isNaN() function. While they serve a similar purpose, the behavior
is very different - the global isNaN() tries to convert its argument into a number before checking if it is NaN. If the
argument cannot be converted into a number, isNaN() will return true, which may not be the desired behavior in all cases.
isNaN('some text'); // true: Number('some text') returns NaN
Number.isNaN('some text'); // false: 'some text' is not NaN
You should use the Number.isNaN() method over isNaN() to perform a strict check for NaN without any type
conversion.
If the intention was not to detect whether a value was NaN, fix the issue by not comparing the variable against itself.
if (value !== anotherValue){
// ...
}
