The JavaScript Payment Request API streamlines the online checkout process by eliminating the need for users to manually input their payment and shipping information, addressing a common issue of cart abandonment due to tedious checkout forms. Acting as an intermediary between the user, merchant, and payment method, the API allows browsers to reuse stored payment and address details, providing a consistent and secure user experience across different websites. This system is part of a broader initiative by the W3C Web Payments Working Group to create a universal standard for web-based transactions, aiming to support various secure payment methods across all browsers and devices. By leveraging a PaymentRequest object, developers can facilitate seamless transactions with the API, enhancing user convenience and potentially increasing conversion rates.