Vue.js - How to properly watch for nested data

Utilizing deep watchers

A frequent scenario in Vue.js apps is location-dependant data, or in simple terms, objects with nested properties. Vue's reactive system can detect changes in these nested properties using a watcher with deep: true. This observes for alterations recursively within an object's nested data.

The strength of Vue.set

When pushing items into an array using native JavaScript methods, Vue cannot detect these changes. Enter Vue.set, a convenient method for adding entries reactively:

methods: {
  addNewItem(item) {
    Vue.set(this.nestedData, this.nestedData.length, item);
  }
}


Think of this as the 'Harry Potter' of array additions. It's doing magic under Vue's invisibility cloak!

Immediate notifications with immediate: true

To execute a callback immediately upon component instantiation, utilize the immediate: true configuration. This awakens the callback function without delay, giving you instant feedback with the current state:

watch: {
  nestedData: {
    immediate: true,
    deep: true,
    handler(newValue, oldValue) {
      console.log('Look who just got updated:', newValue);
    }
  }
}


Embracing dynamic watchers

The $watch API in Vue is a powerful tool when you need to observe a property that isn't determined until runtime:

created() {
  this.$watch(() => this.nestedData.dynamicProperty, (newVal, oldVal) => {
    console.log(`This dynamic property pulls more weight than a contestant in 'The Biggest Loser': ${newVal}`);
  }, { deep: true });
}


Cleanup duty: unwatch

Always remember to unwatch properties when they're no longer required, to prevent potential memory leaks. You've got Vue's inbuilt method for disposing watchers:

let unwatch = this.$watch('nestedData', this.dataChanged, { deep: true });

// The unwatch function, use it to stop the watch when you no longer need it
unwatch();


It's like your Vue's garbage collector, taking care of cleaning up after a party!

Detecting specific nested properties

If keying into specific nested properties is on your radar, use 'object.property' notation in the watch object to keep it focused and efficient:

watch: {
  'nestedData.levelOne.value': function (newValue, oldValue) {
    console.log(`Attention! Value sprinted from: ${oldValue} to ${newValue}. Usain Bolt, is that you?`);
  }
}


Tapping into Vue's reactivity

Familiarize yourself with Vue's reactivity system to supercharge your app's performance. Vue's magic trick involves converting data properties into getters and setters to detect and track changes with maximum efficiency.

Learning from the veterans

Veteran developers in the Vue.js community recommend avoiding deep watchers where possible. They can be performance-hungry monsters and should be used sparingly and only when necessary. Learning from these community code patterns and established best practices can help you avoid common pitfalls and enhance your programming proficiency.