# Interview question: React performance optimization

I get an interview question, which is: <mark>what if there are 10k tasks waiting for process in the front end, how to ensure the tasks does not freeze the page.</mark>

My first thought was web worker, we could create **web worker** and run the tasks on **another thread**, without blocking the main thread that is responsible for **rendering**. (Obviously the task is not related to ui rendering, since web worker have no access to the **DOM**)

While they told me that another solution could be **batch processing**, like using setTimeout(), and there is one more api could be used in this scenario: **requestIdleCallback.** This api would register a callback function and would get it executed when the main thread is idle.

Here is a sample:

```javascript
requestIdleCallback(function(deadline) {
  // check if there is enough idle time in the browser
  while (deadline.timeRemaining() > 0) {
    // execute the task, untill there is no more idle time left
    doSomeTask();
  }
}, {timeout: 2000});  // force execution if the browser is not idle within 2 seconds
```

The final take away from this interview question is that: to ensure the browser remain smooth and doesn’t freeze, the key is to **avoid long-running synchronous tasks** that block the main thread.