What is the purpose of requestIdleCallback?

requestIdleCallback is a browser API that allows functions to be executed during times when the main browser thread is idle. This is useful for performing background tasks with low priority so as not to block the user interface or degrade page responsiveness.

Example usage:

requestIdleCallback(deadline => {
  while (deadline.timeRemaining() > 0 && tasks.length > 0) {
    performTask(tasks.shift());
  }
});

Here, deadline.timeRemaining() indicates how much time is left before the browser becomes busy again, allowing for efficient load distribution without interface delays.