InteropCall

Overview

Calls a JavaScript function through the JS Interop API, providing the best performance for C++ to JavaScript communication. This method is optimized for high-frequency calls and accepts a string argument to pass data to the JavaScript function.

Performance Optimization

InteropCall is specifically designed for performance-critical scenarios where you need to call JavaScript functions frequently. Use this method when performance is more important than flexibility.

Syntax

void InteropCall(
    PrismaView view,
    const char* functionName,
    const char* argument
);

Parameters

view (required)

• Type: PrismaView
• Description: The PrismaView instance in which the function will be called

functionName (required)

• Type: const char*
• Description: The name of the JavaScript function to call
• Note: The function must be globally accessible (e.g., attached to window)

argument (required)

• Type: const char*
• Description: A string argument to pass to the JavaScript function
• Note: Only accepts string data - use JSON for complex data structures

Return Value

This method returns void. Unlike Invoke, InteropCall does not support return value callbacks for maximum performance.

Usage Examples

Basic Function Call

// Simple function call with string argument
PrismaUI->InteropCall(view, "updatePlayerName", "Dragonborn");

// JavaScript function to receive the call
window.updatePlayerName = (playerName) => {
    document.getElementById('player-name').textContent = playerName;
};

High-Frequency Updates

// Performance-critical updates (e.g., health bar)
void UpdateHealthBar() {
    int currentHealth = GetPlayerHealth();
    std::string healthStr = std::to_string(currentHealth);

    // Fast update without callback overhead
    PrismaUI->InteropCall(view, "setHealthValue", healthStr.c_str());
}

// Call this frequently in game loop
void GameLoop() {
    UpdateHealthBar();  // Called every frame
}

// JavaScript - optimized for frequent updates
window.setHealthValue = (health) => {
    // Direct DOM manipulation for best performance
    const healthBar = document.getElementById('health-bar');
    healthBar.style.width = health + '%';
};

JSON Data Transfer

#include <nlohmann/json.hpp>
using JSON = nlohmann::json;

// Send complex data as JSON string
void SendPlayerStats() {
    JSON playerStats = {
        {"health", GetPlayerHealth()},
        {"magicka", GetPlayerMagicka()},
        {"stamina", GetPlayerStamina()},
        {"level", GetPlayerLevel()}
    };

    // Convert to string and send via InteropCall
    std::string jsonStr = playerStats.dump();
    PrismaUI->InteropCall(view, "updatePlayerStats", jsonStr.c_str());
}

// JavaScript - parse JSON data
window.updatePlayerStats = (jsonData) => {
    const stats = JSON.parse(jsonData);

    // Update UI elements
    document.getElementById('health').textContent = stats.health;
    document.getElementById('magicka').textContent = stats.magicka;
    document.getElementById('stamina').textContent = stats.stamina;
    document.getElementById('level').textContent = stats.level;
};

Performance Comparison

When to Use InteropCall

Use InteropCall for frequent updates like position tracking or real-time data. Use Invoke for complex operations that need return values.

Method	Performance	Return Values	Use Case
InteropCall	Highest	No	Frequent updates, real-time data
Invoke	Standard	Yes	Complex operations, one-time calls

Best Practices

String-Only Arguments

InteropCall only accepts string arguments. For complex data, serialize to JSON or use multiple calls with simple string values.

• Performance Critical: Use for high-frequency calls and real-time updates
• String Arguments: Always pass data as strings - use JSON for complex structures
• No Return Values: Don’t expect return values - use RegisterJSListener for bidirectional communication
• Function Availability: Ensure JavaScript functions are globally accessible

Common Issues

Troubleshooting

If InteropCall isn’t working as expected:

• Verify the JavaScript function exists and is globally accessible
• Check that the function name is spelled correctly
• Ensure the argument is properly formatted as a string
• Verify the PrismaView is valid
• Remember that no return values or error feedback is provided

Migration from Invoke

If you’re converting from Invoke to InteropCall for performance:

// Before (using Invoke)
PrismaUI->Invoke(view, "updateHealth(100)");

// After (using InteropCall)
PrismaUI->InteropCall(view, "updateHealth", "100");

// JavaScript function needs to accept argument
// Before
window.updateHealth = () => {
    // Function was called with embedded argument
};

// After
window.updateHealth = (healthValue) => {
    // Function receives argument as parameter
};