isNaN only takes number and does not implement typeguard

[npenin]

TypeScript Version: 2.2.2

Code

var obj='1'

if(!isNaN(obj))
{
   ///here obj should be a number or equivalent
}

Expected behavior:

• isNaN should take any kind of data, not only numbers
• isNaN should implement typeguards so that in the if statement, obj is considered as a number or equivalent

Actual behavior:

• isNaN(obj) breaks on compilation

[RyanCavanaugh]

#12302 / #13227

Please search before logging new issues, both of the things here have been covered before