🕵️ What Are Proxies in JavaScript? (With Practical Use Cases)
Category: js / general-concepts
Difficulty: medium
JavaScript gives you full control over object behavior using a hidden gem: the Proxy. Think of it as a trap-layer between your code and the object it interacts with — letting you intercept reads, writes, deletes, method calls, and more. It’s like Object.defineProperty() on steroids. Let's break it down with surgical clarity. 🔍 What Is a Proxy? A Proxy wraps an object and lets you override fundamental operations. Syntax: [code example] target: the object you want to wrap handler: an object with traps (interceptor methods) ⚙️ Core Concept Here’s a minimal example that logs every property read: [code example] 🧠 Use Case 1: Validation Logic Enforce strict rules when setting object properties. [code example] 🧠 Use Case 2: Auto-Binding Methods Avoid this binding bugs in classes: [code example] Now you can safely extract methods without losing context: [code example] 🧠 Use Case 3: Access Control / Read-Only Make an object read-only: [code example] 🧠 Use Case 4: Array Observation (Reactive Systems) Detect mutations like .push(): [code example] This is foundational to reactivity engines (Vue 2 used Proxies via defineProperty; Vue 3 uses native Proxy). 🧠 Use Case 5: Default Values / Fallbacks Return defaults for missing keys: [code example] ⚠️ Proxy Limitations Slower than direct access (microseconds, but real at scale) Not supported in IE11 (polyfills can't fully replicate) Harder to debug due to indirection JSON.stringify ignores Proxy traps 🧬 Summary ProxyCan Intercept ✅ Method call binding ✅ Enumeration ✅ Object.keys() ✅ | 🧪 Final Thoughts Proxy is one of the most underrated meta-programming tools in JavaScript. It's not for every use case — but when you need full behavioral control, reactive systems, or clean abstractions, it's the scalpel you want. <!-- quiz-start --> Q1: What are the two arguments required when creating a Proxy? [ ] A function and an object [x] A target object and a handler object with traps [ ] A key and a value [ ] An array and a callback fun...