TC39, ECMAScript, and the Future of JavaScript

• how the string 'A' is NaN
• how the string 'A' is not equal to NaN
• how NaN isNaN but is not equal to NaN
• and why introducing Number.isNaN was obviously a very good idea…

isNaN(NaN) // true
isNaN('A') // true
'A' == NaN // false
'A' === NaN // false
NaN === NaN // false

// … solution!

Number.isNaN('A') // false
Number.isNaN(NaN) // true

It explains details about when positive zero is equal to negative zero – and when it isn’t…

+0 == -0 // true
+0 === -0 // true
1/+0 === 1 / -0 // false