Why should you care?

Vue 3 reactivity and some validation libraries use Proxy under the hood.

See it live — copy this example

Paste into an HTML file or the browser console (F12). Use Run below when the live editor is available.

const user = { name: "Ana" };
const observed = new Proxy(user, {
  set(target, key, value) {
    console.log("set", key, value);
    target[key] = value;
    return true;
  }
});
observed.name = "Amy";

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• The set trap runs when you assign.
• You can validate, log, or block changes.

Practice next

1. Run observed set trap logging.
2. Add get trap for reads.
3. Return false from set to reject updates in strict mode.
4. Validate that age cannot be negative inside a set trap.
5. Create read-only proxy that throws on set attempts.

Remember

new Proxy(target, handlers) Traps intercept operations Powers reactive systems

ScriptVerse form model

Proxy logs every field change for audit trail during compliance demo mode.

Outcome: Proxies power reactive state libraries that auto-update UI when data changes.