Lære Proxy Pattern | Structural Patterns

The Proxy pattern is a structural design pattern that lets you provide a surrogate or placeholder for another object to control access to it. In JavaScript, the Proxy object allows you to intercept and customize operations performed on target objects, such as property lookup, assignment, enumeration, function invocation, and more. This pattern is particularly useful when you need to add extra behavior to objects, such as logging, validation, or access control, without modifying the original object directly.

Common scenarios where the Proxy pattern shines include:

Logging every time a property is accessed;
Validating data before it is set on an object;
Restricting access to certain properties based on specific conditions.

By using a proxy, you can separate these concerns from the core business logic of your objects, making your code cleaner and more maintainable.


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const target = {
  message: "Hello, Proxy!"
};

const handler = {
  get: function(obj, prop) {
    console.log(`Property '${prop}' was accessed.`);
    return obj[prop];
  }
};

const proxy = new Proxy(target, handler);

console.log(proxy.message); // Logs: Property 'message' was accessed. Then: Hello, Proxy!

The Proxy pattern is not just about logging property access. You can use it to enforce validation rules before properties are changed, restrict or allow access to certain properties, or implement features like lazy initialization and caching. By intercepting interactions with an object, proxies let you add cross-cutting concerns such as logging or validation in a centralized and reusable way.

1. The Proxy pattern is commonly used to:

2. Which is a typical use case for the Proxy pattern in JavaScript?

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