Understating the 'created' Lifecycle Hook in Vue.js

In Vue.js, one of the key lifecycle hooks is the 'created' hook. Its typical use case is to initialize data, set up event listeners, and start timers. This can be quite useful in the initial step after the instance has been created and the data observation, computed properties, methods, and watchers have all been set up.

Imagine a scenario where you want to fetch data from an external API and update a component's data property after the Vue instance has been created. Since the 'created' hook gets called after the Vue instance has been created, this would be the best place to make the data request and update the component’s data property. Therefore, the 'created' hook plays a crucial role in implementing such initializations in the Vue.js components.

Typically, 'created' lifecycle hook is used like this:

new Vue({
  created() {
    // Initialize data, set up event listeners, and start timers here
  }
})

It's also important to note that during this phase of the lifecycle, the template and virtual DOM have not yet been mounted or rendered. If you need to interact with the DOM or your Vue component’s template, consider using the ‘mounted’ lifecycle hook instead.

It's not recommended to use the 'created' lifecycle hook to manipulate the DOM (since it’s not available at this point), fetch server-side data (since it can lead to unnecessary delays in rendering), or for integrating with other JavaScript libraries (since they might require access to the DOM which isn’t accessible at the 'created' phase).

Understanding the different lifecycle hooks in Vue.js and their appropriate use cases is crucial to building efficient and optimal applications with this JavaScript framework. Remember, each lifecycle hook in Vue.js is designed for specific use-cases and using them correctly can lead to more maintainable and performance-optimized code.