Let’s talk about the process from creation to mounting of a Vue instance

With the continuous development of front-end development, Vue.js, as one of the most popular frameworks in the field of front-end development, is widely used by more and more developers. The core of Vue.js is a Vue instance that allows extension. This article will introduce the process from creation to mounting of this Vue instance.

Creation of Vue instances

Vue instances can be created by calling the Vue constructor and passing in an options object, as shown below:

var vm = new Vue({
  // 选项
})

When instantiating Vue During the process, Vue's initialization process will be executed. Vue's initialization process is a relatively complex process, but it can be described in some simple steps.

First, Vue will merge the incoming option objects, that is, merge the incoming option objects (such as data, methods, etc.) with the option objects inside Vue to form a new option object. If the custom option attributes conflict with Vue's internal option attributes, the custom option attributes will prevail.

Next, Vue will initialize the instance properties. When instantiating Vue, some properties are added to the Vue instance object: $el, $options, $data, etc. Among them, the $el attribute refers to the element mounted by the instance, the $options attribute contains all option attributes in the instance, and the $data attribute contains all responsive data objects in the instance.

Then, Vue will initialize various life cycle functions. During the initialization process of Vue, a series of life cycle functions (such as beforeCreate, created, beforeMount, mounted, etc.) will be executed respectively. These life cycle functions can perform hook function operations on the instance.

Finally, Vue will handle template compilation. During Vue's template compilation process, Vue will convert the template string into a rendering function, and then store the rendering function in the $options property of the instance.

Mounting of Vue instances

After the instantiation process of Vue is completed, the Vue instance will enter the mounting process, that is, the instance will be mounted on an element and displayed. Vue's mounting process mainly consists of several steps.

First, Vue will create a rendering context. During this process, Vue will collect the instance's dependencies (Watcher) and update mechanism to update the view when the data changes.

Next, Vue will create a virtual DOM (Virtual DOM). Virtual DOM is an important means used by Vue to improve rendering efficiency. It is an abstraction of the DOM layer and a lightweight JS object. During the mounting process, Vue will render the virtual DOM generated after the rendering function is executed to the element corresponding to the instance.

Finally, Vue will render and mount the component tree of the instance. During this process, Vue will update the DOM tree where the instance is located based on the virtual DOM, and add, remove, or update element nodes in the DOM tree. The final result is a complete, rendered page.

Summary

From the creation of the Vue instance to the mounting process, we can clearly understand the core mechanism of Vue and how it connects the DOM and data. The creation of a Vue instance includes steps such as merging options, initializing instance properties, processing lifecycle functions, and template compilation, while mounting the instance includes steps such as creating a rendering context, virtual DOM, and rendering and mounting the component tree. Understanding these processes can help us better understand the nature of Vue and develop Vue more efficiently.

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