Vue Watch Props

When working with components in Vue, it's common to pass props down to child components. However, what if you need to watch for changes in these props? That's where Vue's watch functionality comes in.

The Basics

To watch for changes in a prop, you can use the watch property in a component's options. Here's an example:

Vue.component('child-component', {
  props: ['message'],
  watch: {
    message(newValue, oldValue) {
      console.log(`Prop 'message' changed from ${oldValue} to ${newValue}`);
    },
  },
});

In this example, we're watching the message prop and logging any changes to the console.

Computed Properties

Another way to watch for changes in props is to use computed properties. Computed properties can be dependent on props and will update whenever the prop changes. Here's an example:

Vue.component('child-component', {
  props: ['message'],
  computed: {
    messageLength() {
      return this.message.length;
    },
  },
});

In this example, we're using a computed property to watch for changes in the message prop. Whenever the message prop changes, the messageLength computed property will update as well.

Combining Watchers and Computed Properties

You can also combine watchers and computed properties to create more complex functionality. Here's an example:

Vue.component('child-component', {
  props: ['message'],
  data() {
    return {
      reversedMessage: '',
    };
  },
  watch: {
    message(newValue) {
      this.reversedMessage = newValue.split('').reverse().join('');
    },
  },
  computed: {
    messageLength() {
      return this.message.length;
    },
  },
});

In this example, we're using a watcher to update a reversedMessage data property whenever the message prop changes. We're also using a computed property to watch for changes in the message prop and update the messageLength computed property.

Conclusion

By using Vue's watch functionality, you can easily watch for changes in props passed down to child components. And by combining watchers and computed properties, you can create even more complex functionality.