Why isNaN('') or isNaN(“”) is false (one quote or double quotes are considered a valid number)?

Question

I need a built in function that checks if a variable contains a valid number in Javascript , following this link I\'ve tried to use is isNaN , however when I use on

Answer 1

Any thing which cannot be converted to number should return true, But "" string can be parsed to number so it returns false

console.log(+"")
console.log(Number(""))
console.log(isNaN(""))

A polyfill for isNaN looks like this

var isNaN = function(value) {
    var n = Number(value);
    return n !== n;
};

console.log(isNaN(""))

Note:- Things get confusing when you try parseInt on these values. But the parseInt specs literally says it returns NaN the first non-whitespace character cannot be converted to a number. or radix is below 2 or above 36.

console.log(parseInt(""))