Edit a file you did not generate

Use Inject to replace the region between two markers in a file that already exists.

Rendered from docs/how-to/edit-a-file-you-did-not-generate.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.

Inject rewrites the region between two markers in a file that is already there. Use it for the file your generator contributes to rather than owns: a shared config, a registry of routes, a section of a README.

The file to edit is out/routes.js, already carrying its markers:

import { router } from './router.js'

// #--START--#
// #--END--#

export default router

import { Jostraca, Project, Inject, Line, each } from 'jostraca'

const routes = ['health', 'login']

await Jostraca().generate({ folder: './out' }, () => {
  Project({}, () => {
    Inject({
      name: 'routes.js',
      markers: ['// #--START--#\n', '// #--END--#'],
    }, () => {
      each(routes, (route) => {
        Line("router.use('/" + route.val$ + "')")
      })
    })
  })
})

The rewritten routes.js:

import { router } from './router.js'

// #--START--#
router.use('/health')
router.use('/login')
// #--END--#

export default router

The default markers are #--START--#\n and \n#--END--#; give your own pair when the file’s comment syntax needs it. Both are matched literally, so regular-expression metacharacters in a marker are safe, and every matching pair in the file is replaced rather than only the first.

Two failure modes, and they differ:

The file does not exist: Inject throws. It rewrites a file; use File to create one.
The markers are not in the file: nothing happens. The file is left alone and a warning goes to log.debug. No error, no exit code. If you need to know, check the file afterwards, or generate the markers yourself the first time.

Generated content is inserted verbatim, so $&, $1 and $$ in your output survive rather than being interpreted as replacement patterns.

Inject does not honour the exclude option, so a file the user has edited recently is still injected into.

Edit a file you did not generate

See also#