How to Use Proxy Objects in JavaScript

JavaScript objects are incredibly versatile, enabling developers to model real-world data using simple key–value pairs. But what if you could take it further—modify how object access and assignment actually work under the hood? That’s exactly where Proxy Objects come into play.

Whether you're building dynamic APIs, creating logging systems, or enforcing custom validation rules, proxies give you a clean way to intercept and redefine fundamental behaviors in JavaScript objects.

Let’s break it down.

What is a Proxy Object?

Think of a proxy as a stand-in—it behaves like the original thing but adds its own twist. A Proxy Object in JavaScript acts like a middleman between your code and an object, letting you intercept and customize behavior whenever that object is interacted with.

Syntax:

const proxyObject = new Proxy(target, handler);

target: the original object you’re wrapping handler: an object that defines the traps (intercepted operations)

How Do Proxy Objects Work?

Proxy traps intercept internal operations like property access, assignment, and deletion. The most commonly used traps include:

• get: intercepts property access

• set: intercepts property assignments

• deleteProperty: intercepts property deletions

When you perform an action on the proxy, it checks the handler for a trap. If the trap is defined, it runs that instead of the default behavior.

Use Cases of Proxy Objects

1. Logging Property Access

Want to log every time a property is accessed? Proxies make it simple:

const platform = {

type: "peerlist.io",

handle: "sachin87",

};

const proxyPlatformObj = new Proxy(platform, {

get(target, key) {

console.log[Info]: Accessing ${key} at ${Date.now()});

return target[key];

},

});

proxyPlatformObj.type;

// Logs: [Info]: Accessing type at [timestamp]

// Returns: "peerlist.io"

You can even define computed properties dynamically:

const proxyPlatformObj = new Proxy(platform, {
  get(target, key) {
    if (key === "url") {
      return `https://${target.type}/${target.handle}`;
    }
    return target[key];
  },
});

console.log(proxyPlatformObj.url);
// Logs: [Info]: Accessing url at [timestamp]
// Returns: "https://peerlist.io/sachin87"

2. Validation on Property Set
Suppose you want to ensure that the handle is always lowercase and alphanumeric:
const proxyPlatformObj = new Proxy(platform, {
  set(target, key, value) {
    if (key === "handle" && !/^[a-z0-9]+$/.test(value)) {
      console.error(`[Error]: ${key} should be in lowercase and alphanumeric.`);
      return false;
    } else {
      return Reflect.set(target, key, value);
    }
  },
});

proxyPlatformObj.handle = "Sachin87";
// Logs: [Error]: handle should be in lowercase and alphanumeric.

Note the use of Reflect.set() — it lets you maintain the default behavior when you don’t want to override everything manually.

Other Possible Traps

Proxies support many more traps like:

• has

• defineProperty

• ownKeys

• getPrototypeOf

You can explore MDN’s Proxy reference for the complete list and advanced use cases.

Conclusion

Proxy Objects in JavaScript offer powerful capabilities to extend, restrict, or transform the behavior of regular objects. But like all advanced features, they come with complexity. Use them wisely—especially when dealing with team codebases or third-party libraries.

✅ Key takeaways:

• Use Proxies for logging, validation, or API abstraction.

• Don’t overuse them—they can make debugging harder.

• Keep fallback behavior intact using the Reflect API when needed.

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Happy coding! 👩‍💻👨‍💻