Keep a backup when overwriting

Turn on preserve so the bytes you are about to overwrite are kept in a sibling file.

Rendered from docs/how-to/keep-a-backup-when-overwriting.md in the generator repository — where a correction belongs, and where the test suite runs every example on this page or states why it does not.

preserve copies the current file to a .old sibling before writing the new version. It is the cheapest safety net: no merge to reason about, and the user’s work is one mv away.

import { appendFileSync } from 'node:fs'
import { Jostraca, Project, File, Content } from 'jostraca'

const jostraca = Jostraca({
  existing: { txt: { write: true, preserve: true } },
})

const run = (body) => jostraca.generate({ folder: './out' }, () => {
  Project({}, () => File({ name: 'config.sh' }, () => Content(body)))
})

await run('PORT=8080\n')
appendFileSync('./out/config.sh', 'DEBUG=1\n')
await run('PORT=9090\n')

config.old.sh
config.sh

config.old.sh holds what was on disk, edit included:

PORT=8080
DEBUG=1

The suffix goes before the extension, so config.sh becomes config.old.sh and bundle.min.js becomes bundle.min.old.js. A file with no extension appends instead: Makefile becomes Makefile.old, and a dotfile does the same, so .env becomes .env.old.

No backup is written when the content has not changed, so a run that generates the same bytes leaves no .old files behind.

Add write: false to get a snapshot rather than a backup: the copy is taken and the original is left alone.

Backups accumulate, and each run overwrites the previous one. Add *.old.* to the generated project’s .gitignore if the output is checked in.

Keep a backup when overwriting

See also#