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 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

// 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

// 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

// 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