JavaScript 设计模式--缓存代理模式

javascript 缓存代理模式

//缓存代理模式
    var computedFn = function() {
      console.log('begin')
      //console.log(arguments)
      var a = 1
      for(var i = 0; i < arguments.length; i++) {
        a = a * arguments[i]
      }
      return a
    }
    //代理对象
    var proxyComputed = (function(){
       var cache = {}
       return function() {
         //var args = arguments.join(arguments, ',')
         //这里因为arguments只是类数组，不能用数组的[].join()方法
         var args = Array.prototype.join.call(arguments, ',')
         //如果指定的属性在指定的对象或其原型链中，则in运算符返回true
         if(args in cache) {
           console.log('从缓存中取')
           return cache[args]
         }
         //func.apply(thisArg, [argsArray]) ，argsArray可选，类型为数组或者类数组对象
         return cache[args] = computedFn.apply(null, arguments)

         //这样不行，因为computedFn接受参数后会在函数内部合成arguments对象
         //return cache[args] = computedFn(arguments)
       }  
    })()
    console.log(proxyComputed(1, 2, 3, 4))
    console.log(proxyComputed(1, 2, 3, 4))
    console.log(proxyComputed(1, 2, 3, 4))
    //console.log(computedFn(1, 2, 3, 4))
    var trees = new Array("redwood", "bay", "cedar", "oak", "maple");
    console.log(trees)
    console.log("length" in trees)
    console.log(Symbol.iterator in trees)
    console.log("PI" in Math )

    var mycar = {make: "Honda", model: "Accord", year: 1998};
    mycar.make = undefined;
    delete mycar.make
    console.log("make" in mycar);  // 返回true
    console.log("toString" in {})
    console.log({})


    //es6 proxy

    var person = {
      name: '张三'
    }
    var proxy = new Proxy(person, {
      get: function(target, propKey) {
        if(propKey in target){
          return target[propKey]
        } else {
          throw new ReferenceError("Prop name \"" + propKey + "\" does not exist. ")
        }
      }
    })
   console.log(proxy.name) 
   console.log(proxy.age) 

本文由 dealdot ＜dealdot＃163.com＞ 创作, Full Stack Developer @ DeepBlue
本文最后编辑时间为: Apr 20, 2021 at 19:47 pm
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