How to validate digits (including floats) in javascript

Continuing with the @Crescent Fresh approach, some time ago, I had to do number validation, but I needed to verify if a variable contained a number without knowing its type, it could be a String containing a numeric value as in this case, (I had to consider also exponential notation, etc.), a Number object, basically anything I couldn't make any type assumption.

And I had to take care about implicit type conversion, for example as I pointed to @Crescent, isNaN wasn't enough for my case:

// string values
!isNaN(' ') == true;
!isNaN('\t\t') == true;
!isNaN('') == true;

// boolean values
!isNaN(true) == true;
!isNaN(false) == true;

// etc..

I ended up writing a set of 30+ unit tests that you can find and run here, and the following function, is the one that passes all my tests:

function isNumber(n) {
  return !isNaN(parseFloat(n)) && isFinite(n);
}

You don't need regex for this! isNaN will cast thine value to Number:

var valid = !isNaN(value);

Eg:

!isNaN('0'); // true
!isNaN('34.56'); // true
!isNaN('.34'); // true
!isNaN('-34'); // true
!isNaN('foo'); // false
!isNaN('08'); // true

Reluctant Edit (thanks CMS):

Blasted type coercion, !isNaN(''), !isNaN(' '), !isNaN('\n\t'), etc are all true!

Whitespace test + isNaN FTW:

var valid = !/^\s*$/.test(value) && !isNaN(value);

Yuck.

var valid = (value.match(/^-?\d*(\.\d+)?$/));