详解Vue 事件驱动和依赖追踪

class Observer {
 constructor(data) {
  this._data = data;
  this.walk(this._data);
 }

 walk(data) {
  Object.keys(data).forEach((key) => { this.defineRective(data, key, data[key]) })
 };
 defineRective(vm, key, value) {
  var self = this;
  if (value && typeof value === "object") {
   this.walk(value);
  }
  Object.defineProperty(vm, key, {
   get: function() {
    return value;
   },
   set: function(newVal) {
    if (value != newVal) {
     if (newVal && typeof newVal === "object") {
      self.walk(newVal);
     }
     value = newVal;
    }
   }
  })
 }
}

module.exports = Observer;

defineRective(vm, key, value) {
 // 将这个属性的依赖表达式存储在闭包中。
 var dep = new Dep();
 var self = this;
 if (value && typeof value === "object") {
  this.walk(value);
 }
 Object.defineProperty(vm, key, {
  get: function() {
   return value;
  },
  set: function(newVal) {
   if (value != newVal) {
    if (newVal && typeof newVal === "object") {
     self.walk(newVal);
    }
    value = newVal;
    // 通知所有的 viewModel 更新
    dep.notify();
   }
  }
 })
}

class Dep {
 constructor() {
  // 依赖列表
  this.dependences = [];
 }
 // 添加依赖
 addDep(watcher) {
  if (watcher) {
   this.dependences.push(watcher);
  }
 }
 // 通知所有依赖更新
 notify() {
  this.dependences.forEach((watcher) => {
   watcher.update();
  })
 }
}

module.exports = Dep;

var uid = 0;
class Watcher {
 constructor(viewModel, exp, callback) {
  this.viewModel = viewModel;
  this.id = uid++;
  this.exp = exp;
  this.callback = callback;
  this.oldValue = "";
  this.update();
 }

 get() {
  Dep.target = this;
  var res = this.compute(this.viewModel, this.exp);
  Dep.target = null;
  return res;
 }

 update() {
  var newValue = this.get();
  if (this.oldValue === newValue) {
   return;
  }
  // callback 里进行Dom 的更新操作
  this.callback(newValue, this.oldValue);
  this.oldValue = newValue;
 }

 compute(viewModel, exp) {
  var res = replaceWith(viewModel, exp);
  return res;
 }
}

module.exports = Watcher;

Object.defineProperty(vm, key, {
 get: function() {
  var watcher = Dep.target;
  if (watcher && !dep.dependences[watcher.id]) {
   dep.addDep(watcher);
  }
  return value;
 },
 set: function(newVal) {
  if (value != newVal) {
   if (newVal && typeof newVal === "object") {
    self.walk(newVal);
   }
   value = newVal;
   dep.notify();
  }
 }
})

const Observer = require('./Observer.js');
const Watcher = require('./watcher.js');
var data = {
 a: 10,
 b: {
  c: 5,
  d: {
   e: 20,
  }
 }
}

var observe = new Observer(data);

var watcher = new Watcher(data, "a+b.c", function(newValue, oldValue) {
 console.log("new value is " + newValue);
 console.log("oldValue is " + oldValue);
});
console.log("\r\n");
console.log("a has changed to 50,then the expr should has value 55");
data.a = 50;

console.log("\r\n");
console.log("b.c has changed to 50,then the expr should has value 122");
data.b.c = 72;;

console.log("\r\n");
console.log("b.c has reseted an object,then the expr should has value 80");
data.b = { c: 30 }