The GP is referring to doing client side Luhn validation on the credit card number, giving the user feedback if they mistype a number.
It's a technique I use, along with only allowing digits and doing some format masking (i.e. spaces or dashes to split the number into 4 digit blocks) to make the number more readible
Actually, the GP is talking about somehow building a startup based on... form widgets. He specifically said a "(subscription) service" - which would invariably require server-side support for these apparently startup-backed form fields.
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The GP is referring to doing client side Luhn validation on the credit card number, giving the user feedback if they mistype a number.
It's a technique I use, along with only allowing digits and doing some format masking (i.e. spaces or dashes to split the number into 4 digit blocks) to make the number more readible
Actually, the GP is talking about somehow building a startup based on... form widgets. He specifically said a "(subscription) service" - which would invariably require server-side support for these apparently startup-backed form fields.