How To Get Last 4 Digits of A Credit Card Number in Javascript

Recently whilst working on my Aurelia 2 book, for the example application where you checkout I needed to add in the ability to provide a card number and when it saves, the last 4 digits of the card number get saved.

This is one of those things that as developers we won’t do too often, but it’s easy using substr to trim a text string to a certain length.

let ccNumber = '4560265043620583';
let lastFourDigits = ccNumber.substr(-4);

By providing -4 as the value to substr you’re telling it to take the last 4 characters from the string. The result from our example will be 0583. You can also provide non-negative numbers to go from the beginning as well.

I am sure there are other ways of doing the same thing, but I always look for the easiest to read and easiest to understand solutions and substr fits the bill nicely.

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