# Lifecycle ### Introduction An app’s **lifecycle** refers to a cycle where an app starts, runs, and ends. You can create an app’s lifecycle by executing necessary actions in situations **when the app starts, runs, or ends**.

Name	Description
onInit	Function that is called once when running the app the first time
onJoinPlayer	Once onInit is called, the event lets all connected players enter and operates whenever a player enters afterward.
onStart	Function that is called once after each player enters through onJoinPlayer
onUpdate	Function that runs periodically every 20ms
onLeavePlayer	This function causes all players to exit an app when another app is launched or the installed Game Block is destroyed.
onDestroy	Operates when another app is launched or the installed Game Block is destroyed.

### Understanding an App’s Lifecycle Lifecycle functions are necessary as they help create functions according to an app’s life cycle. As you can see in the image below, **Enter-Phase** functions operate when an app starts. When an app is running, **Update-Phase** functions operate periodically, and when it ends, **Exit-Phase** functions start. Make your app’s lifecycle from onInit to onDestroy utilizing the timing of each phrase.

**Lifecycle at a Glance** ```jsx // The first event called when running the app (before the user enters) // Normal and Sidebar apps are called when the map is executed after applying the script [ Enter ] App.onInit.Add(function(){ }); // All players enter the app through this event [ Enter ] // Calls whenever a player enters afterward [ Events ] App.onJoinPlayer.Add(function(player) { }); // Event that starts first when each player enters [ Enter ] App.onStart.Add(function(){ }); // Calls event every 20ms // dt: deltatime (time taken for the previous frame to complete) [ Update ] App.onUpdate.Add(function(dt){ }); // onUpdate again after handling the event callback // Causes all players to leave the app when the app exits [ Exit ] App.onLeavePlayer.Add(function(player){ }); // Last called when an app exits [ Exit ] // Normal app and Sidebar app are closed separately App.onDestroy.Add(function(){ }); ``` ## 1️⃣ Enter-Phase Functions This guides the functions called during the **lifecycle’s Enter Phase** along with the execution of an app. ### onInit {% hint style="info" %} App.onInit.Add(function(){}) {% endhint %} This function is called once when running the app for the first time. **Parameter** * None **Example** Display chat in onInit. (Make this as a Mini-Game to check it out.) ```jsx App.onInit.Add(function(){ App.sayToAll("-- onInit --") App.sayToAll(" ready.. ") App.sayToAll("------------") }); ``` ### onJoinPlayer {% hint style="info" %} App.onJoinPlayer.Add(function(player){}) {% endhint %} Once onInit is called, this event lets all connected players enter and then operates whenever a new player enters afterward. **Parameter**

Name	Type	Description
player	Player	The player who enters The player’s parameter names can be changed arbitrarily

**Example** Display a message when a player enters. ```jsx App.onJoinPlayer.Add(function(player){ App.showCenterLabel(`${player.name} has entered.`) }); ``` ### onStart {% hint style="info" %} App.onStart.Add(function(){}) {% endhint %} This function is called once after players have entered via onJoinPlayer. **Parameter** * None **Example** Display chat in onStart. (Make this as a Mini-Game to check it out.) ```jsx App.onStart.Add(function(){ App.sayToAll("-- App Start --") }); ``` **Understanding the Flow of Enter-Phase Functions** Check **the Enter-Phase lifecycle** flow with codes.\ Make a Mini-Game with the code below and run it! ```jsx // main.js App.onInit.Add(function(){ App.sayToAll("-- onInit --") App.sayToAll(" ready.. ") App.sayToAll("------------") }); App.onJoinPlayer.Add(function(player){ App.sayToAll(`${player.name} has entered.`) }); App.onStart.Add(function(){ App.sayToAll("-- App Start --") }); ```

Figure of Enter-phase functions in sequence

## 2️⃣ Update-Phase Functions Update has an onUpdate function that runs periodically about every 20ms. When an event such as onJoinPlayer or onLeavePlayer occurs, onUpdate is periodically executed again after handling the event. ### onUpdate {% hint style="info" %} App.onUpdate.Add(function(dt){}) {% endhint %} This function runs periodically about every 20ms. **Parameter**

Name	Type	Description
dt	Number	deltatime (time taken for the previous frame to complete, about 20ms) The dt parameter names can be changed arbitrarily

**Example** Make a 10-second timer using the onUpdate function.

```jsx let countdown = 10; let timer = 0; App.onUpdate.Add(function(dt){ timer += dt; if(timer >=1){ if(countdown >= 0) { App.showCenterLabel(countdown--); } else{ App.showCenterLabel("Time Over"); } timer = 0; } }) ``` ## 3️⃣ Exit-Phase Functions These functions execute when an app ends. ### onLeavePlayer {% hint style="info" %} App.onLeavePlayer.Add(function(player){}) {% endhint %} This function operates whenever a player exits. After that, this function kicks all players from the app when another app is launched or the installed Game Block is destroyed. **Parameter**

Name	Type	Description
player	Player	The player who exits The player’s parameter names can be changed arbitrarily

**Example** Display a message when a player exits. ```jsx // Executes when a player exits App.onLeavePlayer.Add(function(player){ App.showCenterLabel(`${player.name} has left.`) }); ``` ### onDestroy {% hint style="info" %} App.onDestroy.Add(function(){}) {% endhint %} It operates when another app is launched or the installed Game Block is destroyed. **Parameter** * None **Example** Display a message when Game Block is destroyed. (Mini-Game)

```jsx // Executes when Game Block is destroyed App.onDestroy.Add(function(){ App.showCenterLabel("Game Block has been destroyed.") }); ``` *** ***