Detailed explanation of Vue.js responsiveness principle-JS Tutorial-php.cn

I come from a Java background. When I first came into contact with JavaScript many years ago, it was a bit strange because it didn’t have getters and setters. Over time, I started to like this missing feature because of the large number of getters and  compared to Java. setter, which makes the code more concise. For example, let's look at the following Java code:

<span style="font-size: 14px;">class Person{<br/>    String firstName;<br/>    String lastName;    // 这个Demo中省略了一些构造器代码 :)    public void setFirstName(firstName) {        this.firstName = firstName;<br/>    }    public String getFirstName() {        return firstName;<br/>    }    public void setLastName(lastName) {        this.lastName = lastName;<br/>    }    public String getLastName() {        return lastName;<br/>    }<br/>}// Create instancePerson bradPitt = new Person();<br/>bradPitt.setFirstName("Brad");<br/>bradPitt.setLastName("Pitt");<br/></span>

JavaScript developers would never do this, instead they would do this:

<span style="font-size: 14px;">var Person = function () {};var bradPitt = new Person();<br/>bradPitt.firstName = &#39;Brad&#39;;<br/>bradPitt.lastName = &#39;Pitt&#39;;<br/></span>

Be concise many. Brevity is usually better, isn't it?

That's true, but sometimes I want to get some properties that can be modified, but I don't have to know what these properties are. For example, we extend a new method getFullName() in Java code:

<span style="font-size: 14px;">class Person{    private String firstName;    private String lastName;    // 这个Demo中省略了一些构造器代码 :)    public void setFirstName(firstName) {        this.firstName = firstName;<br/>    }    public String getFirstName() {        return firstName;<br/>    }    public void setLastName(lastName) {        this.lastName = lastName;<br/>    }    public String getLastName() {        return lastName;<br/>    }    public String getFullName() {        return firstName + " " + lastName;<br/>    }<br/>}<br/><br/>Person bradPitt = new Person();<br/>bradPitt.setFirstName("Brad");<br/>bradPitt.setLastName("Pitt");// Prints &#39;Brad Pitt&#39;System.out.println(bradPitt.getFullName());<br/></span>

In the above example , fullName is a calculated property, it is not a private property, but it always returns the correct result.

C# and implicit getters/setters

Let’s take a look at one of the C# features: implicit getters/setters, I really like it. In C#, if needed, you can define getters/setters, You don't have to do this, but if you decide to do it, the caller doesn't have to call the function. The caller only needs to access the property directly, and getter/setter will automatically Running in the hook function:

<span style="font-size: 14px;">public class Foo {    public string FirstName {get; set;}    public string LastName {get; set;}    public string FullName {get { return firstName + " " + lastName }; private set;}<br/>}<br/></span>

I think this is cool...

Now if I want to implement something like this in JavaScript , I will waste a lot of time, like:

<span style="font-size: 14px;">var person0 = {<br/>    firstName: &#39;Bruce&#39;,<br/>    lastName: &#39;Willis&#39;,<br/>    fullName: &#39;Bruce Willis&#39;,<br/>    setFirstName: function (firstName) {        this.firstName = firstName;        this.fullName = `${this.firstName} ${this.lastName}`;<br/>    },<br/>    setLastname: function (lastName) {        this.lastName = lastName;        this.fullName = `${this.firstName} ${this.lastName}`;<br/>    },<br/>};<br/>console.log(person0.fullName);<br/>person0.setFirstName(&#39;Peter&#39;);<br/>console.log(person0.fullName);<br/></span>

it will print out:

<span style="font-size: 14px;">"Bruce Willis"<br/>"Peter Willis"<br/></span>

but use ## The #setXXX(value) method is not 'JavaScripty' enough (it's a joke).

The following way can solve this problem:

<span style="font-size: 14px;">var person1 = {<br/>    firstName: &#39;Brad&#39;,<br/>    lastName: &#39;Pitt&#39;,<br/>    getFullName: function () {        return `${this.firstName} ${this.lastName}`;<br/>    },<br/>};<br/>console.log(person1.getFullName()); // 打印 "Brad Pitt"<br/></span>

Now we return to the calculated getter. You can set first or last name and simply merge them Value:

<span style="font-size: 14px;">person1.firstName = &#39;Peter&#39;person1.getFullName(); // 返回 "Peter Pitt"<br/></span>

This is indeed more convenient, but I still don't like it because we have to define a function called getxxx() method, which is not 'JavaScripty' enough either. For many years, I've been thinking about how to better use JavaScript.

Then Vue appeared

In my Youtube channel, many videos related to Vue tutorials are mentioned. I am used to responsive development. , in the earlier Angular1 era, we called it: Data Binding. It looks simple. You just need to define some data in the data() block of your Vue instance and bind it to HTML:

<span style="font-size: 14px;">var vm = new Vue({<br/>    data() {<br/>        return {<br/>        greeting: &#39;Hello world!&#39;,<br/>        };<br/>    }<br/>})<div>{greeting}</div><br/></span>

Obviously it will print out "Hello world!" in the user interface.

Now, if you change the value of greeting, the Vue engine will react to this and update accordingly view.

<span style="font-size: 14px;">methods: {<br/>    onSomethingClicked() {        this.greeting = "What&#39;s up";<br/>    },<br/>}<br/></span>

For a long time I was wondering, how does it work? An event is triggered when an object's properties change? Or does Vue keep calling setInterval to check whether it is updated?

After reading the official Vue documentation, I learned that changing an object property will implicitly call getter/ setter, notify the observer again, and then trigger re-rendering, as shown below. This example comes from the official Vue.js document:

Detailed explanation of Vue.js responsiveness principle

但我还想知道：

怎么让数据自带getter/setters？
这些隐式调用内部是怎样的？

第一个问题很简单：Vue为我们准备好了一切。当你添加新数据，Vue将会通过其属性为其添加 getter/setters。但是我让 foo.bar = 3? 会发生什么？

这个问题的答案出现在我和SVG & Vue专家Sarah Drasner的Twitter对话中：

Detailed explanation of Vue.js responsiveness principle

Timo: foo.bar=value;是怎么做到实时响应的？

Sarah: 这个问题很难在Twitter说清楚，可以看这篇文章

Timo: 但这篇文章并没有解释上面提到的问题。

Timo: 它们就像：分配一个值->调用setter->通知观察者，不理解为什么在不使用setInterval和Event的情况下，setter/getter就存在了。

Sarah: 我的理解是：你获取的所有数据都在Vue实例data{}中被代理了。

显然，她也是参考的官方文档，之前我也读过，所以我开始阅读Vue源码，以便更好的理解发生了什么。过了一会我想起在官方文档看到一个叫 Object.defineProperty() 的方法，我找到它，如下：

<span style="font-size: 14px;">/**<br/>* 给对象定义响应的属性<br/>*/export function defineReactive (<br/>    obj: Object,<br/>    key: string,<br/>    val: any,<br/>    customSetter?: ?Function,<br/>    shallow?: boolean<br/>) {    const dep = new Dep()    const property = Object.getOwnPropertyDescriptor(obj, key)    if (property && property.configurable === false) {        return<br/>    }    // 预定义getter/setters    const getter = property && property.get    const setter = property && property.set    let childOb = !shallow && observe(val)<br/>    Object.defineProperty(obj, key, {<br/>        enumerable: true,<br/>        configurable: true,        get: function reactiveGetter () {            const value = getter ? getter.call(obj) : val            if (Dep.target) {<br/>                dep.depend()                if (childOb) {<br/>                    childOb.dep.depend()<br/>                }                if (Array.isArray(value)) {<br/>                    dependArray(value)<br/>                }<br/>            }            return value<br/>        },        set: function reactiveSetter (newVal) {            const value = getter ? getter.call(obj) : val            /* 禁用eslint 不进行自我比较 */            if (newVal === value || (newVal !== newVal && value !== value)) {                return<br/>            }            /* 开启eslint 不进行自己比较 */            if (process.env.NODE_ENV !== &#39;production&#39; && customSetter) {<br/>                customSetter()<br/>            }            if (setter) {<br/>                setter.call(obj, newVal)<br/>            } else {<br/>                val = newVal<br/>            }<br/>            childOb = !shallow && observe(newVal)<br/>            dep.notify()<br/>        }<br/>    })<br/>}<br/></span>

所以答案一直存在于文档中：

把一个普通 JavaScript 对象传给 Vue 实例的 data 选项，Vue 将遍历此对象所有的属性，并使用 Object.defineProperty 把这些属性全部转为 getter/setter。Object.defineProperty 是仅 ES5 支持，且无法 shim 的特性，这也就是为什么 Vue 不支持 IE8 以及更低版本浏览器的原因。

我只想简单的了解 Object.defineProperty() 做了什么，所以我用一个例子简单的给你讲解一下：

<span style="font-size: 14px;">var person2 = {<br/>    firstName: &#39;George&#39;,<br/>    lastName: &#39;Clooney&#39;,<br/>};<br/>Object.defineProperty(person2, &#39;fullName&#39;, {<br/>    get: function () {        return `${this.firstName} ${this.lastName}`;<br/>    },<br/>});<br/>console.log(person2.fullName); // 打印 "George Clooney"<br/></span>

还记得文章开头C#的隐式 getter 吗？它们看起来很类似，但ES5才开始支持。你需要做的是使用 Object.defineProperty() 定义现有对象，以及何时获取这个属性，这个getter被称为响应式——这实际上就是Vue在你添加新数据时背后所做的事。

`Object.defineProperty()`Can Vue become simpler?

After learning all this, I have been thinking, Object.defineProperty() Can I make Vue change More simplified? Nowadays, there are more and more new terms. Is it really necessary to make things too complicated and difficult for beginners to understand (the same is true for Redux):

Mutator: Maybe you are saying (implicitly) setter
Getters: Why not replace Object.defineProperty() with (implicit )getter
##store.commit()： Why not simplify it to foo = bar, but instead store.commit("setFoo", bar);?

#What do you think? Does Vuex have to be complex or can it be as simple as Object.defineProperty()?

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