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doc: add note explaining ESM vs CommonJS startup performance difference #60192

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9 changes: 9 additions & 0 deletions doc/api/esm.md
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Expand Up @@ -331,6 +331,15 @@ syncBuiltinESMExports();

fs.readFileSync === readFileSync;
```
### Performance note

When importing Node.js built-in modules using ESM (for example, `import { STATUS_CODES } from 'http'`),
all properties of the module are eagerly evaluated and added to the namespace at import time.
In contrast, CommonJS (`require('http')`) loads properties lazily when accessed.

This means ESM imports can have slightly higher startup times compared to CommonJS,
especially in short-running scripts or CLI tools.
For long-running applications (e.g., servers), this difference is negligible.

## `import()` expressions

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