In which cases and at what stage is it recommended to optimize JavaScript code in applications running on Node.js?

It is recommended to optimize JavaScript code in Node.js applications after the application has passed the prototyping and basic functionality stage, and performance bottlenecks have been identified. Usually, this occurs during testing or after deployment to production, when metrics and logs are collected.

Optimization is necessary if:

• The server response time is too high.
• High load causes delays.
• Memory is used inefficiently.

Examples of optimization steps:

1. Profiling code using tools (e.g., Node.js Profiler, Clinic.js).
2. Analyzing "hot" functions and bottlenecks.
3. Optimizing algorithms and data structures.
4. Caching results.
5. Asynchronous processing and I/O operation optimization.

Early-stage optimization during development can be premature and complicate the code, so it is important to first ensure that the problem truly exists.