28. What is the purpose of the 'Proxy' object in JavaScript?

Understanding the Proxy Object in JavaScript

The Proxy object in JavaScript is a powerful tool that allows you to customize the behavior of fundamental operations on objects. With a Proxy, you can intercept and redefine operations for an object like property lookup, assignment, enumeration, function invocation, and more.

Basic Usage

A Proxy is created with two parameters:

1. target: The object we are going to wrap.
2. handler: An object with traps that define custom behaviors for operations.

Here is a basic example:

const target = {};
const handler = {
  get: function(obj, prop) {
    return prop in obj ? obj[prop] : `Property ${prop} does not exist`;
  }
};

const proxy = new Proxy(target, handler);

console.log(proxy.someProperty); // Outputs: Property someProperty does not exist

In this example, the get trap is used to intercept property access on the target object. If the property doesn't exist, a custom message is returned.

Use Cases

1. Validation: Proxies can be used to enforce rules on properties of an object.
2. Logging Property Access: You can log each time a property is accessed or modified.
3. Default Values: Automatically provide default values for non-existent properties.
4. Function Argument Manipulation: Modify or validate arguments before they reach the underlying target function.

Important Traps

• get(target, prop, receiver): Intercepts property access.
• set(target, prop, value, receiver): Intercepts property setting.
• has(target, prop): Intercepts the in operator.
• apply(target, thisArg, argumentsList): Intercepts function calls.

Limitations

While Proxy is extremely versatile, it can introduce performance overhead if not used judiciously. It is crucial to consider the complexity and performance implications when designing your application.

Conclusion

The Proxy object unlocks a new level of control over objects and functions in JavaScript, providing capabilities that were previously difficult to achieve. By understanding and applying Proxy, developers can create more robust and flexible applications.