Use requestIdleCallback to schedule JavaScript tasks at an optimal time

JavaScript is single-threaded, which can present some problems when creating an interactive user experience. If JavaScript runs too long while a user is attempting to interact with a page, it can cause noticeable jank or lag, which degrades the experience. requestIdleCallback is a DOM API that allows you to schedule a JavaScript function to be run when the page thread is idle, so your JavaScript doesn't get in the way of the user.