cheesenan

CheeseNaN allows you to truly test if a variable is a number or not. There is a pun intended. You might as well use Number.isFinite or Lodash tbh.

isNaN() is broken

isNaN('') // false
isNaN(' ') // false
 
isNaN(null) // false
isNaN(undefined) // true
 
isNaN(true) // false
isNaN(false) // false
 
isNaN([]) // false
isNaN({}) // true
 
{} + [] // 0
isNaN({} + []) // should be equivalent to isNaN(0), but returns true instead
[] + {} // "[object Object]"
isNaN([] + {}) // true

Number.isNaN() is (less) broken

Number.isNaN('') // false
Number.isNaN(' ') // false
 
Number.isNaN(null) // false
Number.isNaN(undefined) // false
 
Number.isNaN(true) // false
Number.isNaN(false) // false
 
Number.isNaN([]) // false
Number.isNaN({}) // false
 
{} + [] // 0
Number.isNaN({} + []) // false
[] + {} // "[object Object]"
Number.isNaN([] + {}) // false

So here's a convenient test

function cheeseNaN(value) {
    return typeof value !== 'number' || Number.isNaN(value);
}

And now you can do

cheeseNaN('') // true
cheeseNaN(' ') // true
 
cheeseNaN(null) // true
cheeseNaN(undefined) // true
 
cheeseNaN(true) // true
cheeseNaN(false) // true
 
cheeseNaN([]) // true
cheeseNaN({}) // true
 
cheeseNaN({} + []) // true
cheeseNaN([] + {}) // true
 
cheeseNaN(NaN) // true

What's next

• Dunno. Maybe doing something actually usefull?