Optimise This Code for Performance

Analyse and optimise the following code for performance:

```
[paste your code here]
```

Language / runtime: [e.g. Node.js / Python 3.11 / browser JavaScript]
Current performance issue: [e.g. slow response times / high memory usage / blocking the event loop]
Scale context: [e.g. runs 1000x/day / handles 10k concurrent users / processes 1GB files]

Provide:
1. Analysis: identify all performance bottlenecks with explanation of why each is slow
2. Optimised version: rewrite with improvements applied
3. Explanation: for each change, explain what was done and the expected impact
4. Benchmarking suggestion: how to measure the before/after improvement
5. Further optimisations: mention any additional gains possible with infrastructure changes or different approaches