Understanding Vue.js Watchers

Vue.js provides a powerful feature called watchers, which allows you to monitor changes in specific properties of a component’s data and take action accordingly. This blog post will explain how watchers work and provide examples to illustrate their usage.

What are Vue.js Watchers?

A watcher in Vue.js is a special feature that enables you to observe changes in a specific property of a component’s state. It allows you to define a function that will be executed whenever the value of the watched property changes.

Example Usage

Let’s consider an example where we have a Vue component that displays a name and provides a button to change it:

<template>
 <p>My name is {{ name }}</p>
 <button @click="changeName()">Change my name!</button>
</template>

<script>
export default {
  data() {
    return {
      name: 'Flavio'
    }
  },
  methods: {
    changeName() {
      this.name = 'Flavius'
    }
  },
  watch: {
    name() {
      console.log(this.name)
    }
  }
}
</script>

In this example, we have defined a watch object within the Vue component. Inside the watch object, we specify the property we want to watch (name) and assign it to a function. This function will be executed whenever the name property changes.

The function assigned to watch.name can optionally accept two parameters: newValue and oldValue. These parameters represent the new and old values of the watched property, respectively.

<script>
export default {
  /* ... */
  watch: {
    name(newValue, oldValue) {
      console.log(newValue, oldValue)
    }
  }
}
</script>

Limitations

It’s important to note that watchers cannot be referenced or accessed from a template in the same way that computed properties can. Watchers are specifically designed to handle logic related to monitoring changes in data properties.

Conclusion

Vue.js watchers are a useful feature for monitoring changes in specific properties of a component’s state. By using watchers, you can easily execute custom logic whenever a watched property value changes. Understanding and utilizing watchers can help you build more dynamic and responsive Vue.js applications.