How to run VueJS code only after Vue is fully loaded and initialized?

In Vue.js, it is crucial to ensure that Vue is fully loaded and initialized before executing code, especially when working with the DOM or data and methods that depend on the Vue instance. Vue provides several methods to achieve this.

1. Using the mounted Lifecycle Hook

In Vue components, the mounted hook is invoked after the component's template and data have been rendered to the DOM. This makes it the ideal location to execute code once Vue is fully loaded and initialized.

javascript
new Vue({
  el: '#app',
  data() {
    return {
      message: 'Hello Vue!'
    };
  },
  mounted() {
    console.log('The Vue instance has been mounted and is ready for operations!');
    this.doSomething();
  },
  methods: {
    doSomething() {
      // Execute operations requiring Vue to be fully loaded
      console.log(this.message);
    }
  }
});

In this example, the doSomething method runs after the Vue instance is mounted, allowing safe access to data from data and DOM elements.

2. Using Vue.nextTick

When you need to execute operations immediately after Vue completes the DOM update cycle, the Vue.nextTick method enables you to run a delayed callback after the next DOM update cycle. Using this method right after modifying data ensures you can access the updated DOM.

javascript
new Vue({
  el: '#app',
  data: {
    message: 'Hello Vue!'
  },
  methods: {
    updateMessage() {
      this.message = 'Updated message';
      this.$nextTick(function () {
        // DOM is now updated
        console.log('DOM has been updated');
      });
    }
  }
});

Here, the updateMessage method changes the data and uses $nextTick to guarantee execution after the DOM is updated.

3. Using async and await

In Vue 2.5 and above, async functions can be used within mounted and other lifecycle hooks. This allows you to handle asynchronous operations while maintaining clean and readable code.

javascript
new Vue({
  el: '#app',
  data() {
    return {
      message: 'Hello Vue!'
    };
  },
  async mounted() {
    await this.fetchData();
    console.log('Data has been loaded');
  },
  methods: {
    async fetchData() {
      // Simulating an asynchronous data fetch
      await new Promise(resolve => setTimeout(resolve, 1000));
      this.message = 'Data fetched';
    }
  }
});

In this case, the fetchData method simulates an asynchronous data fetch, and the mounted hook uses await to ensure execution only after data is loaded.

By employing these methods, you can effectively manage and sequence asynchronous operations and DOM updates in Vue.js applications, preventing the execution of operations before full initialization and avoiding errors or inconsistent behavior.