ESLint Unexpected use of isNaN

ESLint Unexpected use of isNaN

I’m trying to use the isNaN global function inside an arrow function in a Node.js module but I’m getting this error:
[eslint] Unexpected use of ‘isNaN’. (no-restricted-globals)
This is my code:
const isNumber = value => !isNaN(parseFloat(value));

module.exports = {

Any idea on what am I doing wrong?
PS: I’m using the AirBnB style guide.


Solution 1:

As the documentation suggests, use Number.isNaN.

const isNumber = value => !Number.isNaN(parseFloat(value));

Quoting Airbnb’s documentation:

Why? The global isNaN coerces non-numbers to numbers, returning true
for anything that coerces to NaN. If this behavior is desired, make it

// bad
isNaN('1.2'); // false
isNaN('1.2.3'); // true

// good
Number.isNaN('1.2.3'); // false
Number.isNaN(Number('1.2.3')); // true

Solution 2:

FYI, this will not work for IE.
Check here at browser compatibility.

Solution 3:

In my case, I wanted to treat 5 (integer), 5.4(decimal), ‘5’, ‘5.4’ as numbers but nothing else for example.

If you have the similar requirements, below may work better:

const isNum = num => /^\d+$/.test(num) || /^\d+\.\d+$/.test(num);

//Check your variable if it is a number.
let myNum = 5;

To include negative numbers:

const isNum = num => /^-?\d+$/.test(num) || /^-?\d+\.\d+$/.test(num);

This will remove your issue of global use of isNaN as well.
If you convert the isNum function to a normal ES5 function, it will work on IE browser as well.