仿Vuex响应式源码实现

state响应式原理

我们都知道store里的state是响应式变化的，那是怎么实现的呢？

原理还是利用了Object.defineProperty
Object.keys()方法会返回一个由给定对象的自身可枚举属性组成的数组，数组中属性名的排列顺序和使用for…in循环遍历该对象时返回的顺序一致

代码如下（示例）：

var reactive = obj => {
    let deps = new Dep
    Object.keys(obj).forEach(key => {
        let value = obj[key]  //state.count
        Object.defineProperty(obj, key, {
            get() {
                deps.getters()
                return value
            },
            set(newValue) {
                value = newValue //每次修改值执行
                deps.setters()
            }
        })
    })
    return obj
}

vuex代码如下：

class Store {
    constructor(options = {}) {
        const { state, mutations } = options
        this._vm = reactive(state)
        this._mutations = mutations
    }
    get state() {
        return this._vm
    }
    commit(type, params) {
        const entry = this._mutations[type]
        if (!entry) {
            return
        }
        entry(this.state, params)
    }
}
const store = new Store({
    state: {
        count: 0
    },
    mutations: {
        addCount(state, p) {
            state.count += p
        }
    },
})

var stop = watchEffect(() => {
    var str = `${store.state.count}`
    document.getElementById("app").innerText = str
})
document.getElementById('btn').addEventListener('click', function () {
    store.commit("addCount", 1)
})