Stripe.js is a JavaScript library that you can wire into your checkout form to handle credit card information. When a user signs up using your checkout form, Stripe.js will send the credit card information directly from the user's browser to Stripe's server. 

Stripe.js is a secure option since it ensures that the credit card information doesn't hit your server, thereby minimizing the scope of your PCI compliance.  

There are two ways to implement Stripe.js:

1) Embed Stripe’s form into your checkout page so that your customer can enter both personal and card information. Here's a tutorial on this.

2) Use Stripe’s pop-up form so that your customer enters personal information in your website and card information on the pop-up window that Stripe provides. Here's a tutorial on this.

Either way, the information will be passed directly to Stripe.