---
title: Javascript
description: The build fetches your public policy once and bundles it, so the
  server never fetches it at runtime.
lastModified: "2026-10-12T12:44:54+01:00"
lastAuthor: Christopher Burns
---
The build fetches your public policy once and bundles it, so the server never
fetches it at runtime.

Install `c15t` alongside `@c15t/browser` for the build plugin. Add it to
your existing Vite plugins:

```ts title="vite.config.ts (plugins option)"
import { consentManifest } from 'c15t/build';

export default {
	plugins: [
		// Keep your existing framework plugins here.
		consentManifest({ backendURL: 'https://your-project.inth.app' }),
	],
};
```

Without `backendURL`, the plugin reads `VITE_C15T_BACKEND_URL`, then
`VITE_INTH_PROJECT_URL`. The plugin
fetches the policy during `vite build`, or in `vite dev` when the app first
loads it, and serves it as `snapshot` from `c15t/generated`. A build fetches
only when the app uses `manifest()`. In your browser entry point, pass
`manifest()` as the mode of the existing `init()` call. It reads the snapshot
and the backend URL from `c15t/generated`:

```ts title="src/main.ts"
import { init, manifest } from '@c15t/browser';

init({ mode: manifest() });
```

Keep your scripts and UI options. The browser resolves the snapshot without
a manifest request when the policy does not need geography, or the required
country and region are known through `overrides`. When required
geography is missing, it calls backend `/init` and uses the backend's resolved
policy and translations. Those visitors still wait for a backend round trip
and can receive newer policy than the build snapshot.

When the build has no snapshot, as in `vite dev` after a failed fetch,
`snapshot` is `undefined`, and the browser fetches
`${backendURL}/manifest` instead.

A script-tag site without a build step cannot run this hook.

The snapshot is fixed at build time:

* Rebuild after changing policies, translations or vendors. If your CI caches
  build output, force a fresh build.
* Consent choices still go to the backend.

The build reads the backend URL from your public backend URL variable when
the config doesn't pass one: `NEXT_PUBLIC_C15T_BACKEND_URL` in Next.js,
`NUXT_PUBLIC_C15T_BACKEND_URL` in Nuxt, `PUBLIC_C15T_BACKEND_URL` in Astro,
Svelte and SvelteKit, and `VITE_C15T_BACKEND_URL` in TanStack Start and other
Vite apps. Each also reads the matching Inth variable, such as
`NEXT_PUBLIC_INTH_PROJECT_URL`, when the c15t one is unset. See
[set the backend URL](/docs/concepts/modes#set-the-backend-url).

The fetch waits at most 10 seconds. When it fails, or no backend URL is set,
every framework does the same thing:

|Command|Default when the fetch fails|
|--|--|
|Production build: `next build`, `vite build`, `nuxt build`, `astro build`|The build stops with an error.|
|Dev: `next dev`, `vite dev`, `nuxt dev`, `astro dev`|A warning, and the server fetches the policy at runtime.|

Set `onBuildError` to use one behaviour for both. `'fail'` stops dev too.
`'runtime'` lets a production build finish, and the server fetches the policy
at runtime. The `C15T_ON_BUILD_ERROR` environment variable overrides the
option, so you can deploy during a backend outage without a code change:

```sh
C15T_ON_BUILD_ERROR=runtime npm run build
```

Turborepo's strict environment mode hides undeclared variables from tasks, so
list `C15T_ON_BUILD_ERROR` in the build task's `passThroughEnv` there.

The build skips the fetch, without an error, when it can't use a snapshot,
for example when the backend URL is relative. With `onBuildError: 'fail'`, a
relative URL stops the build. [Consent modes](/docs/concepts/modes#what-happens-when-the-download-fails)
lists every case.

`vite build` and `vite dev` fetch the manifest when they start. `vite preview`
serves the last build without fetching. The plugin writes no file into your
app, so there is nothing to keep out of Git. `c15t/generated` ships its own
types, so `tsc`, `vue-tsc` and `svelte-check` pass on a fresh checkout without
a build first.

The plugin can't see the options your app passes to `manifest()`. When the
app passes `source: 'runtime'` or `manifestURL`, set
`consentManifest({ source: 'runtime' })` too. The build then downloads no
manifest, so it doesn't fail when the backend's `/manifest` is down.

For policy updates without a rebuild, use `hosted()`, which asks the backend's
`/init` on each page load, or `manifest({ source: 'runtime' })`, which fetches
the manifest at runtime. Both keep reading the backend URL from the plugin.