How Can I Effectively Track Variable Changes in JavaScript?

Listening for Variable Changes in JavaScript

In JavaScript, it is common to need to track changes to variables, whether for debugging or other purposes. While older methods like Object.watch and Object.observe are outdated, newer solutions have emerged that provide more robust and effective functionality.

Proxies: A Modern Approach

Introduced in ES6, the Proxy object allows you to wrap an existing object and intercept changes made to its properties. This makes it ideal for monitoring variable changes:

const targetObj = {};
const targetProxy = new Proxy(targetObj, {
  set: (target, key, value) => {
    console.log(`${key} set to ${value}`);
    target[key] = value;
    return true;
  }
});

When you set a property on the proxy object (e.g., targetProxy.hello_world = "test"), the setter function is triggered and logs the change to the console.

Observing Complex Objects

Proxies are not always suitable for nested objects. For these cases, libraries like Observable Slim offer specialized solutions. Observable Slim creates a reactive wrapper around your object, tracking changes and firing events when they occur:

const test = { testing: {} };
const p = ObservableSlim.create(test, true, (changes) => {
  console.log(JSON.stringify(changes));
});

p.testing.blah = 42; // Logs properties and changes in JSON format

Considerations

• Proxies are not fully supported in older browsers.
• Special objects like Dates may not behave as expected with proxies.
• For complex objects, specialized libraries like Observable Slim are recommended.

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