Understanding the 'el' Property in Vue.js

The 'el' property in a Vue instance is used to specify the HTML element that the Vue instance will be mounted onto. The Vue instance takes control of the DOM element specified by the 'el' property, meaning it becomes a manage point where Vue can work to update the DOM when data changes.

The 'el' property can specify any valid CSS selector, such as an element id, a class name, or a tag name. While using a specified id as the 'el' property is the most common approach, Vue.js is flexible and can adapt to your specific needs.

For instance, to mount a Vue instance to a div with the id 'app', you would write:

new Vue({
  el: '#app',
});

In this example, the Vue.js instance will control the HTML element with the id 'app'. This way, any changes made to the data within the Vue.js app will be reflected in this HTML element.

In practical applications, this allows you to define a Vue.js application that controls only a specific portion of your HTML page - leaving the rest of the page to be managed by other JavaScript libraries, plain HTML, or even other Vue.js applications. This makes the use of Vue.js highly flexible and adaptable to existing codebases without needing a complete overhaul to integrate Vue.js.

It's important to note that only one Vue instance should be attached to an individual DOM element. Creating multiple Vue instances that control the same DOM element can result in unexpected behavior. This underlines the broader best practice in Vue - each Vue instance should have a clear and unambiguous scope of control, and different instances can interact and share data via components and props.

In summary, the 'el' property defines the scope of a Vue.js instance, serving as a control point where Vue can manage the DOM. It is one of the fundamental aspects of creating a Vue.js app.