The interviewer suddenly asked: What is the difference between Vue2 and Vue3?

Preface

Nowadays, there are crazy rumors on the Internet that the front-end is dead. In fact, the essential reason is that personnel have increased and positions have decreased, which has led to increased competitive pressure.

We have no way to solve the existing problems in society, but we can start from ourselves to increase our competitiveness.

When multiple people compete for a position, there is actually no difference between the second place and the last place, because they only want the first place.

So it is very important to answer every question to 100 points!

This is also the reason why I wrote "One Question Confuses the Interviewer".

This topic hopes to help everyone get 100 points in each question and "conquer" the interviewer in the shortest time. Cherish every interview opportunity in your hand, and wish you all to join your favorite company with high salary as soon as possible

How should you answer when asked "The difference between vue2 and vue3"

Vue Internally based on functions Can be divided into three large modules: Responsivenessreactivite, Runtimeruntime, Editorcompiler, and some smaller ones function points. So to talk about the difference between vue2 and vue3, we need to start with these three aspects and add smaller functional points.

First of all, let’s talk about Responsivenessreactivite:

vue2’s responsiveness mainly depends on Object.defineProperty Implementation, but Object.defineProperty can only monitor the getter behavior and setter behavior of the specified property of the specified object, then This can cause problems in some cases.

What's the problem?

For example: we declared an object person in data, but added new attributes to person later, then this New properties will lose responsiveness. It is actually very simple to solve this problem. You can use the Vue.$set method to increase the responsiveness of the specified attribute of the specified object. But such a method is unreasonable in Vue's automatic responsiveness mechanism.

So in Vue3, Vue introduces the concepts of reflection and proxy. The so-called reflection refers to Reflect, and the so-called proxy refers to Proxy. We can use Proxy to directly proxy a common object and get a proxy instance proxy object. In vue3, this process is implemented through the reactive method.

But proxy can only implement proxy complex data types, so vue provides an additional ref method to handle responses of simple data types sex. ref In essence, it does not monitor data, but builds a RefImpl class, which is marked # through set and get ##value Function is implemented in this way. So ref must be triggered through .value. The essence of this is to call the value method.

Next is

runtimeruntime:

The so-called runtime, most of the time refers to

renderer renderer, the renderer is essentially an object, with three main internal methods render, hydrate, createApp, among which render mainly handles rendering logic, hydrate mainly handles services End rendering logic, and createApp is the method to create vue instances.

Here we mainly talk about the

render rendering function. In order to ensure the separation of the host environment and rendering logic, all logic related to the host environment is extracted in vue3 separated, passed through the form of interface. The purpose of this is actually to unbind the host environment and rendering logic to ensure that vue can render normally in a non-browser host environment.

Further down is

Editorcompiler: compiler

in

vue is actually A DSL (dedicated language editor in a specific domain), whose purpose is to compile the template template into a render function. The logic is mainly divided into three major steps: parse, transform and generate. The function of parse is to convert template into AST (Abstract Syntax Tree) , transform can convert AST (Abstract Syntax Tree) Syntax tree) is converted into JavaScript AST, and finally generate converts JavaScript AST into render function . The transformation process will involve some slightly complex concepts, such as Finite Automatic State Machine which will not be discussed here.

In addition, there are some other changes. For example, vue3’s new composition API. composition API will have some different presentations in vue3.0 and vue3.2, for example: the original composition API starts with setup The function serves as the entry function. setup The function must return two types of values: the first is an object, and the second is a function.

When the setup function returns an object, the data or methods in the object can be used in template. When a setup function returns a function, the function is treated as a render function.

But the form of this setup function is not good, because all the logic is concentrated in the setup function, and it is easy to have a huge setup Function, we call it the Boulder (Shit Mountain) function. So in vue 3.2, a new syntax sugar of script setup was added to try to solve this problem. At present, the presentation of script setup is still very good.

In addition, there are some small changes, such as Fragment, Teleport, Suspense, etc. I won’t go into details...

Recommended learning: 《vue.js video tutorial》