Proxy in javascript. Advance JS

Using proxy you can intercept the fundamental functions for objects.

What are fundamental functions?

When you do myObject.anyKey it will invoke get function and when you do

myObject.anyOtherKey = "Some Value"

you are invoking set function.

All functions that you can intercept are mentioned here

How you can intercept ?

let obj = {hello:'world'}
let proxyObj= new Proxy( obj, {
   get: function( target, key, context ) {
   // you are intercepting get now
    return "SOMETHING ELSE"
   }
});
console.log(proxyObj.hello) // SOMETHING ELSE
console.log(obj.hello) // world

But if you want to keep default behaviour and also count number of times properties of obj is accessed.

let obj = {hello:'world'}
let coundObjPropertiesUsed = 0
let proxyObj= new Proxy( obj, {
   get: function( target, key, context ) {
    // you are intercepting get now
   coundObjPropertiesUsed++
    return target[key]
   }
});
console.log(proxyObj.hello) // world
console.log(obj.hello) // world
console.log(coundObjPropertiesUsed) // 1

target is the object Proxy is called upon. ( in this case obj)

What is the use case?

1. You can use it in logging
2. to get how many times function is called

let fibonacci = n => n <= 1 ? n :fibonacci( n - 1 ) + fibonacci( n - 2 );
let fibCalls = 0;
fibonacci = new Proxy( fibonacci, {
 apply: function( target, thisValue, args ) {
 fibCalls += 1;
 return target(...args);
}});
fibonacci( 12 );
console.log( 'fibCalls:', fibCalls );

above fibCalls will contain number of time function fibonacci was called.

Thats all for now. Hope you have learn something new today from this article.