---
id: vanilla/api/stift
title: Stift instance
---

What the instance does after construction, grouped by concern. Translating has its own page; everything stateful lives here.

## Locale

- `getLocale(): RegisteredLocale` — the active locale, narrowed to your registered union.
- `getDirection(): 'ltr' | 'rtl'` — derive `dir` attributes from this, never the tag.
- `setLocale(locale): void` — reactive switch, persists the preference to `state`.
- `subscribe(fn): () => void` — store subscription; the returned function unsubscribes.
- `detectLocale(ctx?): Promise<RegisteredLocale>` — runs `detection.order` (`'persisted'` reads the stored preference).

## Boot and packs

- `initialize({ locale?, critical? }): Promise<void>` — swaps to the target locale and loads per `loadingStrategy`; resolves once the `critical` namespaces are ready.
- `installLocale(locale, namespaces?): Promise<boolean>` / `activateLocale(locale): Promise<boolean>` / `isLocaleInstalled(locale): Promise<boolean>` — the offline install lifecycle.
- `getPackSize(locale): Promise<PackSizeInfo>` — byte-accurate download accounting.
- `pack: PackManager` — staleness checks and refresh; the offline guide owns the detail.

## Params and units

- `setParam(name, value): void` — typed override against the declared `values`, persisted unless `persist: false`. `resetParam(name)` / `resetAllParams()` drop overrides.
- `setUnit(category, unit): void` — typed override, validated and persisted. `resetUnit(category)` / `resetAllUnits()` drop overrides.
- `getUnits(): Partial<Record<UnitCategory, string>>` — the effective per-category record. `getUnitValues(category)` lists the allowed values for a picker.

## Examples

```ts
// Backend-driven personalization: push the value in, it persists locally.
await stift.setLocale(user.locale)
stift.setParam('gender', user.gender)
```

## Next

- Translating → [Translating](./translate.md)
- Detection order and boot modes → [Setup & Boot](../setup.md)
- Pack lifecycle → [Offline & Persistence](../../runtime/offline-persistence.md)