What Is the Recommended JavaScript Execution Time to Minimize First Input Delay (FID), and How Can I Ensure Efficient Execution?


To minimize First Input Delay (FID) in JavaScript, the main task duration should be kept under 50 milliseconds. To ensure efficient JavaScript execution, it's important to break up long tasks, optimize your code, leverage browser APIs, and implement Web Workers.

Main Task Duration

Google's recommendation is to keep main thread work under 50 milliseconds to achieve fast responsiveness and maintain smooth interaction [Entering Interactivity, Google, 2021].

Ensuring Efficient Execution

Breaking Up Long Tasks

Long tasks, which involve executing JavaScript for more than 50ms non-stop, block the main thread and cause FID issues. By breaking up these tasks into smaller, asynchronous tasks, you can minimize the impact on responsiveness and interactivity [Optimize JavaScript Execution, Google, 2021].

Optimizing Your Code

Efficiency is critical. Optimize your JavaScript code by leveraging modern syntax, eliminating unnecessary computations, caching, memoization, and using efficient data structures and algorithms [Time to Interactive, Google, 2020].

Browser APIs

Offload tasks to the browser where possible. Utilize APIs like `IntersectionObserver` for lazy-loading, `requestIdleCallback` for scheduling non-essential work, and `WebAssembly` for computationally intensive tasks [JavaScript Promises: an Introduction, Google, 2021].

Web Workers

JavaScript is single-threaded, which can limit the efficiency of code execution. Web Workers allow you to run JavaScript on background threads, freeing up the main thread to remain responsive to user input [Using Web Workers, MDN, 2021].


Keeping main task duration under 50ms, breaking up long tasks, optimizing code, using Browser APIs efficiently, and implementing Web Workers are all strategies that can help reduce First Input Delay and ensure efficient JavaScript execution.