js技巧之十几行的代码实现vue.watch代码

(function () {
  var o = { a : 1}//声明一个对象,包含一个 a 属性,值为1
  Object.defineProperty(o,"b",{
    get: function () {
      return this.a;
    },
    set : function (val) {
      this.a = val;
    },
    configurable : true
  });

  console.log(o.b);//==> 1
  o.b = 2;
  console.log(o.b);//==> 2
})();

import watcher from './watcher.js';
let wm = new watcher({
  data:{
    a: 0 
  },
  watch:{
    a(newVal,oldVal){
      console.log('newVal:'+newVal);
      console.log('oldVal:'+oldVal);
    }
  }
})
vm.a = 1 
// newVal:1
// oldVal:0

class watcher{
  constructor(opts){
    this.$data = opts.data;
    for(let key in opts.data){
      this.setData(key,opts.data[key])
    }
  }

  setData(_key,_val){
    Object.defineProperty(this,_key,{
      get: function () {
        return this.$data[_key];
      },
      set : function (val) {
        const oldVal = this.$data[_key];
        if(oldVal === val)return val;
        this.$data[_key] = val;
        return val;
      },
    });
  }
}

export default watcher;

/**
 * @desc 属性改变监听，属性被set时出发watch的方法，类似vue的watch
 * @author Jason
 * @date 2018-04-27
 * @constructor 
 * @param {object} opts - 构造参数. @default {data:{},watch:{}};
 * @argument {object} data - 要绑定的属性
 * @argument {object} watch - 要监听的属性的回调 
 * watch @callback (newVal,oldVal) - 新值与旧值 
 */
class watcher{
  constructor(opts){
    this.$data = this.getBaseType(opts.data) === 'Object' ? opts.data : {};
    this.$watch = this.getBaseType(opts.watch) === 'Object' ? opts.watch : {};
    for(let key in opts.data){
      this.setData(key)
    }
  }

  getBaseType(target) {
    const typeStr = Object.prototype.toString.apply(target);
  
    return typeStr.slice(8, -1);
  }

  setData(_key){
    Object.defineProperty(this,_key,{
      get: function () {
        return this.$data[_key];
      },
      set : function (val) {
        const oldVal = this.$data[_key];
        if(oldVal === val)return val;
        this.$data[_key] = val;
        this.$watch[_key] && typeof this.$watch[_key] === 'function' && (
          this.$watch[_key].call(this,val,oldVal)
        );
        return val;
      },
    });
  }
}

export default watcher;

let wm = new watcher({
  data:{
    a: 0,
    b: 'hello'
  },
  watch:{
    a(newVal,oldVal){
      console.log(this.b);
    }
  }
})

 btn1.onclick=function(){
  var a = 'haha';
  document.getElementById('id').innerHTML = a;
 }
 btn2.onclick=function(){
  var a = 'xixi';
  document.getElementById('id').innerHTML = a;
 }
let wm = new watcher({
  data:{
    a: "",
  },
  watch:{
    a(newVal,oldVal){
      document.getElementById('id').innerHTML = newVal;
    }
  }
})

btn1.onclick=function(){
  wm.a = 'haha';
 }
 btn2.onclick=function(){
  wm.a = 'xixi';
 }