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The Complete Guide to Modern JavaScript

Proxies

Learn how to define custom behaviors for fundamental operations with Proxies.

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What is a Proxy?

From MDN:

The Proxy object is used to define custom behavior for fundamental operations (e.g. property lookup, assignment, enumeration, function invocation, etc).

 

How to use a Proxy ?

This is how we create a Proxy:

var x = new Proxy(target,handler)
  • our target can be anything, from an object, to a function, to another Proxy
  • a handler is an object which will define the behavior of our Proxy when an operation is performed on it
Node.js
// our object
const dog = { breed: "German Shephard", age: 5}
// our Proxy
const dogProxy = new Proxy(dog, {
  get(target,breed){
    return target[breed].toUpperCase();
  },
  set(target, breed, value){
    console.log("changing breed to...");
    target[breed] = value;
  }
});
console.log(dogProxy.breed);
// "GERMAN SHEPHARD"
console.log(dogProxy.breed = "Labrador")
// changing breed to...
// "Labrador"
console.log(dogProxy.breed);
// "LABRADOR"

When we call the get method, we step inside the normal flow and ...

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