Why does isNaN(" ") (string with spaces) equal false?

In JavaScript, why does isNaN(" ") evaluate to false, but isNaN(" x") evaluate to true?

I’m performing numerical operations on a text input field, and I’m checking if the field is null, "", or NaN. When someone types a handful of spaces into the field, my validation fails on all three, and I’m confused as to why it gets past the isNaN check.

Solution 1:

JavaScript interprets an empty string as a 0, which then fails the isNAN test. You can use parseInt on the string first which won't convert the empty string to 0. The result should then fail isNAN.

Solution 2:

You may find this surprising or maybe not, but here is some test code to show you the wackyness of the JavaScript engine.

document.write(isNaN("")) // false
document.write(isNaN(" "))  // false
document.write(isNaN(0))  // false
document.write(isNaN(null)) // false
document.write(isNaN(false))  // false
document.write("" == false)  // true
document.write("" == 0)  // true
document.write(" " == 0)  // true
document.write(" " == false)  // true
document.write(0 == false) // true
document.write(" " == "") // false

so this means that

" " == 0 == false

and

"" == 0 == false

but

"" != " "

Have fun :)

Solution 3:

To understand it better, please open Ecma-Script spec pdf on page 43 "ToNumber Applied to the String Type"

if a string has a numerical syntax, which can contain any number of white-space characters, it can be converted to Number type. Empty string evaluates to 0. Also the string 'Infinity' should give

isNaN('Infinity'); // false

Solution 4:

Try using:

alert(isNaN(parseInt("   ")));

Or

alert(isNaN(parseFloat("    ")));