# Startup and lifecycle

> Lia.init, Lia.ready, Lia.session and Lia.close, and every event Lia sends your page. From the Lia developer docs: https://docs.lialabs.org/reference/sdk-lifecycle

### Lia.init()

Call it first. It answers with who the player is and everything about how your app is shown, and fills in the SDK's [properties](/reference/sdk#properties) and CSS variables.

```js
const me = await Lia.init();
```

Resolves with:

| Field | Type | What it is |
| --- | --- | --- |
| `player` | object | `{ id, name }`: the player's id in your app, and their Lia username. See [Players](/concepts/players-and-sessions). |
| `session` | string | A session token for your server, `lias_…`. |
| `exp` | number | When the session ends, in milliseconds since 1970 (15 minutes after opening). |
| `mode` | string | `"test"` or `"live"`. |
| `language` | string | The person's language in Lia, such as `"en"`. |
| `rtl` | boolean | Whether it reads right to left. |
| `platform` | string | `"ios"` or `"android"`. |
| `theme` | string | `"light"` or `"dark"`. |
| `themeParams` | object | Lia's colours (`bg_color`, `text_color`…). |
| `display` | string | `"sheet"`, `"full"` or `"fullscreen"`. |
| `isFullscreen` | boolean | Edge to edge or not. |
| `viewport` | object | `{ height, expanded }` |
| `safeArea` | object | `{ top, bottom, left, right }` in px |
| `contentSafeArea` | object | `{ top, bottom, left, right }` in px |
| `startParam` | string or null | What your app was opened with. |
| `link` | string | Your app's invite link, without a startParam. |
| `sound` | boolean | Whether the person wants your app's sounds. |
| `notifications` | object | `{ allowed, available }`: whether they allowed your notifications, and whether your app may ask. |

Errors: `not_in_lia`, `not_ready` (Lia is still opening the app; try again shortly), `timeout`.

### Lia.ready()

Tells Lia your page is drawn, so it takes its loader away. Call it once your first screen is on the page. Returns nothing.

```js
Lia.init().then(function (me) {
  renderHome(me);
  Lia.ready();
});
```

### Lia.session()

A fresh session token for your server. Sessions last 15 minutes, so get a new one before calls your server must trust.

```js
const { session, exp } = await Lia.session();
```

Resolves with `{ session, exp }`. Errors: `not_open` (the person hasn't opened your app in Lia yet; call `init()` first), `timeout`.

### Lia.close()

Closes your app. Resolves with `null`. If you turned on [closing confirmation](/reference/sdk-layout#lia-enableclosingconfirmation), this closes without asking.

### Lia.on(event, listener)

Listens for one of Lia's events. Returns a function that stops listening.

```js
const stop = Lia.on("theme", function (data) { redraw(data.colorScheme); });
// later
stop();
```

Throws `bad_listener` if `listener` isn't a function. A listener that throws doesn't stop the others.

### Lia.off(event, listener)

Stops a listener added with `Lia.on`.

### Lia.onPause(listener)

The same as `Lia.on("pause", listener)`. Returns a function that stops listening.

### Lia.onResume(listener)

The same as `Lia.on("resume", listener)`.

## Events

| Event | Data | When |
| --- | --- | --- |
| `"pause"` | none | Lia went to the background, or one of Lia's screens (the pay sheet, an ad, a dialog) covered your app. Pause timers and sound. |
| `"resume"` | none | Back again. |
| `"theme"` | `{ theme, colorScheme }` | The person switched Lia between light and dark. `theme` is the new colours. CSS variables are already updated. |
| `"viewport"` | `{ height, expanded, isStateStable }` | Your page's height changed (a sheet pulled up, bottom buttons shown). |
| `"fullscreenChanged"` | `{ isFullscreen, contentSafeArea }` | Your app went to or from fullscreen. |
| `"languageChanged"` | `{ language, rtl }` | The person changed Lia's language. |
| `"startParam"` | `{ startParam }` | A notification or invite for your app was opened while it was already open. |
| `"notificationsChanged"` | `{ allowed }` | The person allowed or stopped your app's notifications. |
| `"soundChanged"` | `{ on }` | The person muted or unmuted your app from Lia's ⋯ menu. |
| `"charge"` | `{ chargeId, productId }` | A payment was confirmed while no `Lia.pay()` was waiting (after a reload). Also `Lia.onCharge`. |
| `"ad"` | `{ state, format }` | An ad's stage: `"loading"`, `"showing"` or `"closed"`. Also `Lia.onAd`. |
| `"mainButtonClicked"` | none | The main button was pressed. Also `Lia.mainButton.onClick`. |
| `"secondaryButtonClicked"` | none | The secondary button was pressed. |
| `"backButtonClicked"` | none | The header's back button was pressed. |
| `"settingsButtonClicked"` | none | Settings was chosen in the ⋯ menu. |
| `"accelerometerChanged"` | `{ x, y, z }` | A reading, while the accelerometer runs. |
| `"gyroscopeChanged"` | `{ x, y, z }` | A reading, while the gyroscope runs. |
| `"deviceOrientationChanged"` | `{ alpha, beta, gamma }` | A reading, while orientation runs. |
| `"accelerometerStarted"`, `"accelerometerStopped"` | none | The sensor started or stopped. Also for `gyroscope` and `deviceOrientation`. |

The SDK updates its own properties (`Lia.colorScheme`, `Lia.viewport`, `Lia.language`, `Lia.soundOn` and the rest) before your listeners run.