Detect Array Changes: How to Watch Arrays in Javascript - Quick Guide

  1. Introduction
  2. Using the "Proxy" Object
  3. Conclusion


Arrays are a fundamental data type in JavaScript, used to store lists of values. In some cases, it can be useful to detect changes to an array and take action accordingly. In this quick guide, we'll explore how to watch arrays in JavaScript and detect changes.

Using the "Proxy" Object

One way to watch for changes to an array is by using the "Proxy" object in JavaScript. A "Proxy" object allows you to intercept and customize operations performed on an object, including array operations like "push", "pop", "shift", and "unshift".

Here's an example:

const myArray = ["apple", "banana", "cherry"];
const arrayHandler = {
  set: function(target, property, value) {
    console.log(`Array changed: ${property}=${value}`);
    target[property] = value;
    return true;
const proxyArray = new Proxy(myArray, arrayHandler);


In this example, we create a "Proxy" object for the "myArray" array. We define a "handler" object with a "set" method that logs a message to the console whenever an array operation is performed. Finally, we create a "proxyArray" object that uses the "myArray" array as its target and the "arrayHandler" object as its handler.

When we call the "push" method on the "proxyArray" object, the "set" method in the "arrayHandler" object is called, and we see the message "Array changed: 3=orange" logged to the console.


Watching arrays in JavaScript can be accomplished using the "Proxy" object and a custom "handler" object. By intercepting array operations with the "set" method, you can detect changes to the array and take action accordingly. This technique can be useful in a variety of scenarios, such as data binding in web applications.

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