What are watchers in Vue 3 and how do I use them?

What are watchers in Vue 3 and how do I use them?

Watchers in Vue 3 are a way to observe changes in data properties and react to those changes. You can use them to perform asynchronous operations or to perform side effects when a data property changes.

Can you give me an example of how to set up a watcher?

Sure! Here's a simple example:

import { ref, watch } from 'vue';

const count = ref(0);

watch(count, (newValue, oldValue) => {
  console.log(`Count changed from ${oldValue} to ${newValue}`);
});

In this example, whenever count changes, the watcher will log the old and new values.

What if I want to watch multiple properties?

You can watch multiple properties by using an array in the watcher. For example:

watch([property1, property2], ([newProp1, newProp2], [oldProp1, oldProp2]) => {
  console.log(`Property1 changed from ${oldProp1} to ${newProp1}`);
  console.log(`Property2 changed from ${oldProp2} to ${newProp2}`);
});

Are there any performance considerations I should be aware of?

Yes, excessive watchers can lead to performance issues, especially if they trigger heavy computations or API calls. It's best to keep watchers focused and only use them when necessary.