Vue响应式原理剖析

Vue响应式原理代码

const data = {
  name: 'mushan',
  age: 18,
  shan: {
    name: '木杉',
    age: 18,
    obj: {}
  },
  arr: [1, 2, 3]
}

const arrayProto = Array.prototype;
const arrayMethods = Object.create(arrayProto);
['push', 'pop', 'shift', 'unshift' ,'sort', 'splice', 'reverse'].forEach(method => {
  arrayMethods[method] = function () {
    arrayProto[method].call(this, ...arguments);
    render();
  }
})

function defineReactive (data, key, value) {
  observer(value);
  Object.defineProperty(data, key, {
    get () {
      return value;
    },
    set (newVal) {
      if(value === newVal) {
        return;
      }
      value = newVal;
      render();
    }
  })
}

function observer (data) {
  if(Array.isArray(data)) {
    data.__proto__ = arrayMethods;
    return;
  }

  if(typeof data === 'object') {
    for(let key in data) {
      defineReactive(data, key, data[key])
    }
  }
}

function render () {
  console.log('页面渲染啦');
}

function $set (data, key, value) {
  if(Array.isArray(data)) {
    data.splice(key, 1, value);
    return value;
  }
  defineReactive(data, key, value);
  render();
  return value;
}

function $delete(data, key) {
  if(Array.isArray(data)) {
    data.splice(key, 1);
    return;
  }
  delete data[key];
  render();
}

observer(data);

 

利用vue2中Object.defineProperty实现响应式的劣势

1. 天生就需要进行递归
2. 监听不到数组不存在的索引的改变
3. 监听不到数组长度的改变
4. 监听不到对象的增删