Bits of .NET

🛡️ Proxy = Object Interception

Objects are exposed. Proxy intercepts operations. Validation, logging, reactivity, access control.

📝 Proxy Basics

// Basic proxy
const target = { name: 'Alice', age: 30 };
const handler = {
    get: function(obj, prop) {
        console.log(`Getting ${prop}`);
        return obj[prop];
    },
    set: function(obj, prop, value) {
        console.log(`Setting ${prop} to ${value}`);
        obj[prop] = value;
        return true;
    }
};
const proxy = new Proxy(target, handler);
proxy.name; // Logs: Getting name
proxy.age = 31; // Logs: Setting age to 31

// Validation proxy
const userValidator = {
    set: function(obj, prop, value) {
        if (prop === 'age') {
            if (typeof value !== 'number' || value < 0 || value > 120) {
                throw new Error('Invalid age');
            }
        }
        if (prop === 'email') {
            if (!value.includes('@')) {
                throw new Error('Invalid email');
            }
        }
        obj[prop] = value;
        return true;
    }
};
const user = new Proxy({}, userValidator);
user.age = 30; // OK
user.email = 'test@example.com'; // OK
// user.age = -5; // Throws Error

// Read-only proxy
const readOnlyHandler = {
    set: function(obj, prop, value) {
        throw new Error(`Cannot modify ${prop}`);
    }
};
const config = new Proxy({ apiKey: 'secret' }, readOnlyHandler);
// config.apiKey = 'new'; // Throws Error

🎯 Advanced Proxy

// Reactive proxy (Vue-like)
function reactive(obj) {
    return new Proxy(obj, {
        get(target, key) {
            // Track dependency
            track(target, key);
            return target[key];
        },
        set(target, key, value) {
            target[key] = value;
            // Trigger updates
            trigger(target, key);
            return true;
        }
    });
}

// Auto-generate getters/setters
class AutoProxy {
    constructor(target) {
        return new Proxy(target, {
            get: function(obj, prop) {
                if (prop in obj) return obj[prop];
                console.warn(`Property ${prop} doesn't exist`);
                return undefined;
            }
        });
    }
}

💡 Proxy Use Cases

• Validation
• Reactivity (Vue, Svelte)
• API caching
• Logging
• Access control