Understanding the 'Created' Lifecycle Hook in Vue.js

Vue.js uses a series of lifecycle hooks to allow users to add their own code at specific stages. When it comes to fetching data during the creation of a component, the 'created' lifecycle hook is the ideal choice.

This is because the 'created' lifecycle hook gets triggered early in the lifecycle, right after the Vue instance has been created. It's perfect for fetching data because, at this point in the lifecycle, the component’s data and events have been initialized, but the $el property and the template or render function have not.

Let's look at a practical example to further clarify how this works:

new Vue({
  data() {
    return {
      fetchedData: null
    }
  },
  created() {
    fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(data => {
        this.fetchedData = data;
      });
  }
});

In this example, you can see that we're using the 'created' hook to fetch data from an API. The data returned from the API is stored to the 'fetchedData' property which is part of our Vue component's data.

The reason we don't use the other lifecycle hooks for data fetching is as follows:

• The 'beforeCreate' hook is called before the initialization of the component’s data and events, making it unsuitable for data fetching.
• The 'mounted' hook is called after the Vue instance has been mounted, which may lead to unnecessary delay in fetching the data and can even cause empty data being rendered initially.
• The 'beforeMount' hook is called just before the instance is mounted onto the DOM, but it runs after the render function has been compiled. Fetching data in this hook could lead to unnecessary re-rendering.

As a best practice, it's recommended to use the lifecycle hooks responsibly to optimize your application. If you're fetching data in the 'created' hook, remember that it runs before the Vue instance has been mounted, so if you need to access the DOM, do so in the 'mounted' hook instead.

Knowing how to properly use lifecycle hooks in Vue.js is vital to building efficient, high-quality applications. By effectively leveraging them according to the specific needs of your project, you can greatly improve the performance and user experience of your Vue.js apps.