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

javascript nan
IVR Avenger picture IVR Avenger · May 5, 2009 · Viewed 70.2k times · Source

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.

Answer

Antonio Haley picture Antonio Haley · May 5, 2009

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.

Related questions

How do you check that a number is NaN in JavaScript?

I’ve only been trying it in Firefox’s JavaScript console, but neither of the following statements return true: parseFloat('geoff') == NaN; parseFloat('geoff') == Number.NaN;

Read More
How to turn NaN from parseInt into 0 for an empty string?

Is it possible somehow to return 0 instead of NaN when parsing values in JavaScript? In case of the empty string parseInt returns NaN. Is it possible to do something like that in JavaScript to check for NaN? var value = parseInt(…

Read More
Why does typeof NaN return 'number'?

Just out of curiosity. It doesn't seem very logical that typeof NaN is number. Just like NaN === NaN or NaN == NaN returning false, by the way. Is this one of the peculiarities of javascript, or would there be a reason …

Read More