Vue data中随意改一个属性,视图都会更新吗?

new Vue({
  el: '#app',
  data() {
    return {
      a: 1,
      b: 2,
      c: 3,
      d: 4,
    };
  },
  created() {
    console.log(this.b);
    this.b = 'aaa';
  },
  template: '<div>Hello World{{a}}{{b}}</div>',
});

const keys = Object.keys(data)
  const props = vm.$options.props
  const methods = vm.$options.methods
  let i = keys.length
  while (i--) {
    const key = keys[i]
    if (props && hasOwn(props, key)) {
      process.env.node_ENV !== 'production' && warn(
        `The data property "${key}" is already declared as a prop. ` +
        `Use prop default value instead.`,
        vm
      )
    } else if (!isReserved(key)) {
      // 代理对象的属性
      proxy(vm, `_data`, key)
    }
  }
  // observe data
  observe(data, true )

observe(data, true );

// observe
const keys = Object.keys(obj);
for (let i = 0; i < keys.length; i++) {
  defineReactive(obj, keys[i]);
}

// defineReactive
Object.defineProperty(obj, key, {
  enumerable: true,
  configurable: true,
  get: function reactiveGetter() {
    const value = getter ? getter.call(obj) : val;
    // 重点在这里，后续如果在模板中使用到的属性，都会被执行reactiveGetter函数
    // 被Dep类 收集起来
    if (Dep.target) {
      console.log(`${key} 属性 被Dep类收集了`)
      dep.depend();
      if (childOb) {
        childOb.dep.depend();
        if (Array.isArray(value)) {
          dependArray(value);
        }
      }
    }
    return value;
  },
  set: function reactiveSetter(newVal) {
    const value = getter ? getter.call(obj) : val;
    
    if (newVal === value || (newVal !== newVal && value !== value)) {
      return;
    }
    if (setter) {
      // 这里是处理computed set 函数
      setter.call(obj, newVal);
    } else {
      val = newVal;
    }
    childOb = !shallow && observe(newVal);
    // 如果我们在更改属性时，就会调用notify 异步更新视图
    dep.notify();
  },
});

if (vm.$options.el) {
  vm.$mount(vm.$options.el);
}

Vue.prototype.$mount = function (
  el?: string | Element,
  hydrating?: boolean
): Component {
  el = el && query(el);

  const options = this.$options;
  // resolve template/el and convert to render function
  
  if (!options.render) {
    let template = options.template;
    if (template) {
      if (typeof template === 'string') {
        if (template.charAt(0) === '#') {
          template = idToTemplate(template);
          
          if (process.env.NODE_ENV !== 'production' && !template) {
            warn(
              `Template element not found or is empty: ${options.template}`,
              this
            );
          }
        }
      } else if (template.nodeType) {
        template = template.innerhtml;
      } else {
        if (process.env.NODE_ENV !== 'production') {
          warn('invalid template option:' + template, this);
        }
        return this;
      }
    } else if (el) {
      // 如果模板不存在，就创建一个默认的html模板
      template = getOuterHTML(el);
    }
  }
  // 重写了Vue.prototype.$mount ，最终调用缓存的mount方法完成对$mount的挂载
  return mount.call(this, el, hydrating);
};

const { render, _parentVnode } = vm.$options;
vnode = render.call(vm._renderProxy, vm.$createElement);