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I focused my self in the mobile version of the challenge. My questions are about the form validation part: 1)how do I check if the input value is empty? with ' input.value == "" ' or ' input.value == null '? there are some differences? 2)how do I 'force' the space between the numbers in the card number input? I mean both while writing and when I show it in the interactive card.

Thanks for help, any other tip is welcome.

Hi, that's my solution on the challenge. I submitted a non-finished version in order to receive feedback on the grid layout. Thanks for helping!

I have some questions:

• I still don't understand why sometimes "getElementById" works, and sometimes not. So the question is why this happen.
• I had some issues with the input manipulation, in particoular with the custom tip input. How can I set it on focus when it appears?
• Again with the custom tip input, why my program doesn't gets the input value?

Thanks for helping.

ps. I tried the 'mobile first approach' and it's a lot easier

updates:

• I figured out that the "custom button" can be replaced by an input with a placeholder="Custom"