ES6 Proxy实现Vue的变化检测

Vue变化检测Object使用DefineProperty、数组使用方法拦截实现。最近，Vue3.0将采用ES6 Proxy的形式重新实现Vue的变化检测，在官方还没给出新方法之前，我们先实现一个基于Proxy的变化检测。

模块划分

参照之前Vue变化检测的代码，将Vue 变化检测的功能分为以下几个部分。

• Observer
• Dep
• Watcher
• Utils

首先，我们要确定的问题是，将Dep依赖搜集存在哪里。Vue 2.x里，Object的依赖收集放在defineRactive，Array的依收集存入到Observer中。ES6 Proxy里，考虑到让handler访问dep，我们将依赖放入到Observer中。

Observer

observer.js功能代码如下：

import Dep from './dep';
import { isObject } from './utils';

export default class Observer {
    constructor (value) {
        // 递归处理子元素
        this.obeserve(value);
        // 实现当前元素的代理
        this.value = this.proxyTarget(value);
    }
    
    proxyTarget (targetBefore, keyBefore) {
        const dep = new Dep();
        targetBefore.__dep__ = dep;
        let self = this;
        const filtersAtrr = val => ['__dep__', '__parent__'].indexOf(val) > -1;
        return new Proxy(targetBefore, {
            get: function(target, key, receiver){
                if (filtersAtrr(key)) return Reflect.get(target, key, receiver);
                if (!Array.isArray(target)) {
                    dep.depend(key);
                }
                // sort/reverse等不改变数组长度的，在get里触发
                if (Array.isArray(target)) {
                    if ((key === 'sort' || key === 'reverse') && target.__parent__) {
                        target.__parent__.__dep__.notify(keyBefore);
                    }
                } 
                return Reflect.get(target, key, receiver);
            },
            set: function(target, key, value, receiver){
                if (filtersAtrr(key)) return Reflect.set(target, key, value, receiver);
                // 新增元素，需要proxy
                const { newValue, isChanged } = self.addProxyTarget(value, target, key, self);
                // 设置key为新元素
                Reflect.set(target, key, newValue, receiver);
                // notify
                self.depNotify(target, key, keyBefore, dep, isChanged);
                return true;
            },
        });
    }

    addProxyTarget(value, target, key, self) {
        let newValue = value;
        let isChanged = false;
        if (isObject(value) && !value.__parent__) {
            self.obeserve(newValue);
            newValue = self.proxyTarget(newValue, key);
            newValue.__parent__ = target;
            isChanged = true;
        }
        return {
            newValue,
            isChanged,
        }
    }

    depNotify(target, key, keyBefore, dep, isChanged) {
        if (isChanged && target.__parent__) {
            target.__parent__.__dep__.notify(keyBefore);
            return;
        }
        if (Array.isArray(target)) {
            if (key === 'length' && target.__parent__) {
                target.__parent__.__dep__.notify(keyBefore);
            }
        } else {
            dep.notify(key);
        }
    }

    obeserve(target) {
        // 只处理对象类型，包括数组、对象
        if (!isObject(target)) return;
        for (let key in target) {
            if (isObject(target[key]) && target[key] !== null) {
                this.obeserve(target[key]);
                target[key] = this.proxyTarget(target[key], key);
                // 设置__parent__,方便子元素调用
                target[key].__parent__ = target;
            }
        }
    }
}


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在Observer中，针对对象，只需要执行 dep.depend(key) 、 dep.notify(key) 即可。添加 key 是为了能正确的触发收集，不知道怎么说明白为什么要这样做，只能一切尽在不言中了。

Array, 如何实现依赖的收集和触发那。依赖收集与Object类似， dep.depend(key) 完成数组的收集。关于触发，可以分为两个方面，一是改变数组长度、二未改变数组长度的。改变数组长度的，在set里，通过长度属性的设置触发父级元素的notify。为什么要使用父级元素的notify那？我们可以分析以下，在你设置数组的长度时，这时候的target\key\value分别是[]\length*, 这个时候，数组的依赖收集是没有的，你watcher的是数组，并不是数组本身。这个时候只能通过 target.__parent__.__dep__.notify(keyBefore) 触发父级的收集，完成数据变化的检测。二对于未改变数组长度的，这里的做法，虽然是直接 target.__parent__.__dep__.notify(keyBefore) 触发依赖，但是有个严重的问题，实际上更新的数据不是最新的，这个地方暂时还没想到比较好的方法，欢迎大家讨论。

Dep

Dep.js

let uid = 0;

export default class Dep {
    constructor () {
        this.subs = {};
        this.id = uid++;
    }

    addSub(prop, sub) {
        this.subs[prop] = this.subs[prop] || [];
        this.subs[prop].push(sub);
    }

    removeSub(prop, sub) {
        this.remove(this.subs[prop] || [], sub);
    }

    depend(prop) {
        if (Dep.target) {
            // 传入的是当前依赖
            Dep.target.addDep(prop, this)
        }
    }

    notify(prop) {
        const subs = (this.subs[prop] || []).slice();
        for (let i = 0, l = subs.length; i < l; i++) {
            subs[i].update();
        }
    }

    remove(arr, item) {
        if (arr.length) {
            const index = arr.indexOf(item);
            if (index > -1) {
                return arr.splice(index, 1);
            }
        }
    }
}

Dep.target = null
const targetStack = []

export function pushTarget (_target) {
    if (Dep.target) targetStack.push(Dep.target)
    Dep.target = _target
}

export function popTarget () {
    Dep.target = targetStack.pop()
}
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dep 添加prop实现类型的绑定，为什么要这么做那？使用proxy代理后，你假如wahcter对象下的几个元素，此时的deps将同时存在这几个元素，你触发依赖的时候，这些依赖都会执行。因此，通过key值绑定观察事件，触发时，能完成对象的正确触发。

watcher、utils

import { parsePath } from './utils';
import { pushTarget, popTarget } from './dep'

export default class Watcher {
    constructor(vm, expOrFn, cb) {
        // dep id集合
        this.depIds = new Set();
        
        this.vm = vm;
        this.getter = parsePath(expOrFn);
        this.cb = cb;
        this.value = this.get();
    }

    get () {
        pushTarget(this);

        let value = this.getter.call(this.vm, this.vm);
        popTarget();

        return value;
    }

    update() {
        const oldValue = this.value;
        this.value = this.get();
        this.cb.call(this.vm, this.value, oldValue);
    }

    addDep (prop, dep) {
        const id = dep.id;
        if (!this.depIds.has(id)) {
            this.depIds.add(id);
            dep.addSub(prop, this);
        }
    }
}
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utils.js

/**
 * 解析简单路径
 */

const bailRE = /[^\w.$]/;
export function parsePath (path) {
    if (bailRE.test(path)) {
        return;
    }
    const segments = path.split('.');
    return function (obj) {
        for (let i = 0; i < segments.length; i++) {
            if (!obj) return;
            obj = obj[segments[i]];
        }
        return obj;
    };
}

/**
 * Define a property.
 */
export function def (obj, key, val, enumerable) {
    Object.defineProperty(obj, key, {
        value: val,
        enumerable: !!enumerable,
        writable: true,
        configurable: true
    })
}

/**
 * Quick object check - this is primarily used to tell
 * Objects from primitive values when we know the value
 * is a JSON-compliant type.
 */
export function isObject (obj) {
    return obj !== null && typeof obj === 'object'
}

/**
 * Check whether an object has the property.
 */
const hasOwnProperty = Object.prototype.hasOwnProperty
export function hasOwn (obj, key) {
  return hasOwnProperty.call(obj, key)
}
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Utils.js/Watchers.js与Vue 2.x类似，这里就不多介绍了。

测试一下

test.js

import Observer from './observer';
import Watcher from './watcher';

let data = {
    name: 'lijincai',
    password: '***********',
    address: {
        home: '安徽亳州谯城区',
    },
    list: [{
        name: 'lijincai',
        password: 'you know it Object',
    }], 
};

const newData = new Observer(data);

let index = 0;
const watcherName = new Watcher(newData, 'value.name', (newValue, oldValue) => {
    console.log(`${index++}: name newValue:`, newValue, ', oldValue:', oldValue);
});

const watcherPassword = new Watcher(newData, 'value.password', (newValue, oldValue) => {
    console.log(`${index++}: password newValue:`, newValue, ', oldValue:', oldValue);
});

const watcherAddress = new Watcher(newData, 'value.address', (newValue, oldValue) => {
    console.log(`${index++}: address newValue:`, newValue, ', oldValue:', oldValue);
});

const watcherAddressHome = new Watcher(newData, 'value.address.home', (newValue, oldValue) => {
    console.log(`${index++}: address.home newValue:`, newValue, ', oldValue:', oldValue);
});

const watcherAddProp = new Watcher(newData, 'value.addProp', (newValue, oldValue) => {
    console.log(`${index++}: addProp newValue:`, newValue, ', oldValue:', oldValue);
});

const watcherDataObject = new Watcher(newData, 'value.list', (newValue, oldValue) => {
    console.log(`${index++}: newValue:`, newValue, ', oldValue:', oldValue);
});

newData.value.name = 'resetName';
newData.value.password = 'resetPassword';
newData.value.name = 'hello world name';
newData.value.password = 'hello world password';
newData.value.address.home = 'hello home';
newData.value.address.home = 'hello home2';
newData.value.addProp = 'hello addProp';
newData.value.addProp ={
    name: 'ceshi',
};
newData.value.addProp.name = 'ceshi2';

newData.value.list.push('1');
newData.value.list.splice(0, 1);
newData.value.list.sort();
newData.value.list.reverse();
newData.value.list.push('1');
newData.value.list.unshift({name: 'nihao'});
newData.value.list[0] = {
    name: 'lijincai',
    password: 'you know it Array',
};
newData.value.list[0].name = 'you know it array after';
newData.value.list.pop();
newData.value.list.shift();
newData.value.list.length = 1;
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我们使用对象、数组测试一下我们的ES6 Proxy检测。

20:17:44.725 index.js?afc7:20 0: name newValue: resetName , oldValue: lijincai
20:17:44.725 index.js?afc7:24 1: password newValue: resetPassword , oldValue: ***********
20:17:44.725 index.js?afc7:20 2: name newValue: hello world name , oldValue: resetName
20:17:44.725 index.js?afc7:24 3: password newValue: hello world password , oldValue: resetPassword
20:17:44.726 index.js?afc7:32 4: address.home newValue: hello home , oldValue: 安徽亳州谯城区
20:17:44.726 index.js?afc7:32 5: address.home newValue: hello home2 , oldValue: hello home
20:17:44.726 index.js?afc7:36 6: addProp newValue: hello addProp , oldValue: undefined
20:17:44.727 index.js?afc7:36 7: addProp newValue: Proxy {name: "ceshi", __dep__: Dep, __parent__: {…}} , oldValue: hello addProp
20:17:44.727 index.js?afc7:40 0: newValue: Proxy {0: Proxy, 1: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", __dep__: Dep, __parent__: {…}}
20:17:44.728 index.js?afc7:40 1: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}
20:17:44.729 index.js?afc7:40 2: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}
20:17:44.731 index.js?afc7:40 3: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}
20:17:44.734 index.js?afc7:40 4: newValue: Proxy {0: "1", 1: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", 1: "1", __dep__: Dep, __parent__: {…}}
20:17:44.735 index.js?afc7:40 5: newValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}}
20:17:44.735 index.js?afc7:40 6: newValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}}
20:17:44.736 index.js?afc7:40 7: newValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", 2: "1", __dep__: Dep, __parent__: {…}}
20:17:44.737 index.js?afc7:40 8: newValue: Proxy {0: Proxy, 1: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: Proxy, 1: "1", __dep__: Dep, __parent__: {…}}
20:17:44.738 index.js?afc7:40 9: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}
20:17:44.738 index.js?afc7:40 10: newValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}} , oldValue: Proxy {0: "1", __dep__: Dep, __parent__: {…}}
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我们看到了ES6 Proxy后实现了Object/Array的检测，虽然还存在一些问题，但是基本的侦测变化的功能都已经具备了。