---
title: "Extract part of a template"
description: "Use eject to take one marked region out of a larger template file."
source: "https://jostraca.org/how-to/extract-part-of-a-template/"
---

# Extract part of a template

Use eject to take one marked region out of a larger template file.

Rendered from [`docs/how-to/extract-part-of-a-template.md`](https://github.com/jostraca/jostraca/blob/master/docs/how-to/extract-part-of-a-template.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.

Sometimes the file you want to borrow from is a working file—one that compiles, or runs, or that somebody maintains for its own sake—and you want one region of it. `eject` takes the region between two markers and discards everything else, markers included.

The template is `tpl/example.js`, a file that works on its own:

```js
import { setup } from './harness.js'

// EXTRACT-START
export function handler(req) {
  return { ok: true }
}
// EXTRACT-END

setup(handler)
```

Take just the middle:

```js
import { Jostraca, Project, File, Fragment } from 'jostraca'

await Jostraca().generate({ folder: './out' }, () => {
  Project({}, () => {
    File({ name: 'handler.js' }, () => {
      Fragment({
        from: '../tpl/example.js',
        eject: ['// EXTRACT-START\n', '// EXTRACT-END\n'],
      })
    })
  })
})
```

The generated `handler.js`:

```js
export function handler(req) {
  return { ok: true }
}
```

The markers themselves are removed, so the extracted region needs no cleaning up afterwards.

`eject` is forgiving in one direction only, and silently: if either marker is missing from the file, or the end marker comes before the start, or you pass a one-element array, the **whole** source is used instead. There is no error. Check the output the first time, and pin it with a test if the template is maintained by somebody else.

Both markers may be regular expressions instead of strings, which is what you want when the region boundary varies.

## See also

-   [Fill a template file’s slots](https://jostraca.org/how-to/fill-a-template-slot) when you want to put content into the template rather than take content out.
-   [Component reference](https://jostraca.org/docs/reference-components#fragment) for the rest of `Fragment`’s props.