# JavaScript Execution & Communication

## Goal

Execute JavaScript code in the WebView and retrieve results for Unity-WebView interaction.

## Actions Required

| Action                                  | Purpose                    |
| --------------------------------------- | -------------------------- |
| WebViewCreateInstance                   | Creates WebView instance   |
| WebViewLoadURL                          | Loads web content          |
| WebViewShow                             | Displays WebView           |
| WebViewRunJavaScript                    | Executes JS code           |
| WebViewGetRunJavaScriptResult           | Retrieves JS result        |
| WebViewGetRunJavaScriptError (optional) | Retrieves JS error details |

## Variables Needed

* webViewInstance (Object): Stores the WebView instance
* targetURL (String): URL to load
* jsScript (String): JavaScript code to execute
* jsResult (String): Result from JavaScript execution

## Implementation Steps

### 1. State: CreateAndLoadWebView

Follow Use Case 1 (Basic Browser) to create, load, and show WebView. Wait for `WebViewOnLoadFinish` success before executing JavaScript.

### 2. State: ExecuteJavaScript

**Action:** WebViewRunJavaScript

* **Inputs:**
  * webViewInstance → From variable
  * script → jsScript variable
* **Events:**
  * successEvent → GetResult
  * failureEvent → GetError (optional) / ShowError

**Example Scripts:**

* Get page title: `"document.title"`
* Get element value: `"document.getElementById('username').value"`
* Call function: `"myFunction('param1', 'param2')"`
* Modify DOM: `"document.body.style.backgroundColor = 'red'"`

### 3. State: GetResult

**Action:** WebViewGetRunJavaScriptResult

* **Outputs:**
  * result → jsResult variable
* **Next:** ProcessResult

### 4. State: ProcessResult

Use the retrieved JavaScript result in Unity (display, save to PlayerPrefs, trigger game logic, etc.)

### Optional: State: GetError

**Action:** WebViewGetRunJavaScriptError

* **Outputs:**
  * errorCode / errorDescription → Use for UI/logging

## Common Issues

* **JavaScript doesn't execute**: Ensure page has finished loading (wait for OnLoadFinish)
* **Result is empty**: Check that JavaScript actually returns a value
* **Security errors**: Some websites block external JavaScript execution
* **Timing issues**: JavaScript must be enabled with `WebViewConfigure(javaScriptEnabled=true)`

## Flow Diagram

```
CreateWebView → LoadURL → Show
    ↓
WaitForLoad (OnLoadFinish success)
    ↓
ExecuteJavaScript
    ├─ Success → GetResult → ProcessResult
    └─ Failure → ShowError
```

## Best Practices

* Wait for page load completion before executing JavaScript
* Test JavaScript in browser console first to verify syntax
* Handle empty/null results gracefully
* Use JSON.stringify() in JavaScript to return complex objects as strings
* Parse JSON strings in Unity using JsonUtility or similar

## Example Use Cases

### Extract User Input

```javascript
// JavaScript to execute
jsScript = "document.getElementById('email').value"

// Result processing
ProcessResult state:
  - Store jsResult in PlayerPrefs
  - Validate email format
  - Continue to next game state
```

### Modify Page Appearance

```javascript
// Change background color
jsScript = "document.body.style.backgroundColor = '#FF5733'; 'success'"

// Hide ads
jsScript = "document.querySelectorAll('.ad').forEach(el => el.style.display = 'none'); 'hidden'"
```

### Get Page Data

```javascript
// Get all link URLs
jsScript = "JSON.stringify(Array.from(document.querySelectorAll('a')).map(a => a.href))"

// Result is JSON array string
ProcessResult state:
  - Parse jsResult with JsonUtility
  - Display links in Unity UI
```

### Call Website Functions

```javascript
// Login through website's JavaScript API
jsScript = "loginUser('username', 'password'); 'login_initiated'"

// Get game state from web game
jsScript = "JSON.stringify(gameState.getCurrentLevel())"
```

## Advanced: Bidirectional Communication

For ongoing communication, combine with Custom URL Schemes (Use Case 3):

1. **Unity → WebView**: Use `WebViewRunJavaScript`
2. **WebView → Unity**: Website calls `window.location = 'unity://callback?data=value'`
3. **Unity receives**: Via `WebViewOnURLSchemeMatchFound` listener

## JavaScript Debugging

If JavaScript fails:

1. Enable `WebViewConfigure(javaScriptEnabled=true)` first
2. Test script in browser DevTools console
3. Check for syntax errors in script string
4. Verify page elements exist (use browser inspector)
5. Use simple `"'test'"` script to verify execution works

## Security Considerations

* Only execute JavaScript on trusted websites
* Validate and sanitize any user input passed to JavaScript
* Be aware that JavaScript can access cookies and local storage
* Some content security policies may block external script execution


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