Guide to Monitoring Object Property in a Vue Extension

Introduction

Let's look at a basic plugin setup:

import SomeObject from "./SomeObject";

/**
 * Simple Plugin Example...
 */
export default {
    install(Vue){

        Vue.prototype.$someObject = Vue.observable(SomeObject);

    }
}

The goal here is to make an object reactive across the entire application.

Issue and Query

Vue.prototype.$someObject has properties that require global level watching, not just within components.

Is it possible to add a watcher to the Vue instance in the install method of a Vue plugin?

Note: I am seeking a solution other than the one below as it defeats the purpose of plugin separation. Additionally, a global mixin won't suffice...

watch: {

    '$someObject.foo': {
        handler(value) {
            console.log(value);
        }
    }

}

Attempts so far

Referring to the documentation linked here, I tried these approaches:

export default {
    install(Vue){

        Vue.prototype.$someObject = Vue.observable(SomeObject);

        // Here are the methods I tested:
        Vue.watch(Vue.prototype.$someObject.foo, value => { console.log(value) });
        Vue.$watch(Vue.prototype.$someObject.foo, value => { console.log(value) });
        Vue.prototype.watch(Vue.prototype.$someObject.foo, value => { console.log(value) });
        Vue.prototype.$watch(Vue.prototype.$someObject.foo, value => { console.log(value) });

        Vue.watch(Vue.$someObject.foo, value => { console.log(value) });
        Vue.$watch(Vue.$someObject.foo, value => { console.log(value) });
        Vue.prototype.watch(Vue.$someObject.foo, value => { console.log(value) });
        Vue.prototype.$watch(Vue.$someObject.foo, value => { console.log(value) });

    }
}

Answer №1

If you're working with Vue 2, you'll find that only Vue instances expose the watch feature. However, once Vue 3 is released, you'll have more options available. For now, you'll need to stick with using a Vue instance.

But don't worry, you can still achieve what you want by incorporating an instance within your plugin:

import Vue from 'vue';
import SomeObject from './SomeObject';

/**
 * A Cool Plugin...
 */
export default {
    install (Vue) {
        Vue.prototype.$someObject = Vue.observable(SomeObject);

        new Vue({
          watch: {
            '$someObject.foo' () {
              // Do something
            }
          }
        })
    }
}

The Vue instance created here isn't intended for rendering purposes. It's solely used to facilitate watching $someObject.

Although you mentioned ruling out this approach in the question, it's worth considering creating a dedicated Vue instance specifically for watching purposes.

Another option would be to utilize property setters instead of watch. This involves using Object.defineProperty to create setters for the properties you want to monitor, and then triggering any necessary side effects within the setter function.

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