前不久在参加面试的时候遇到了这样一道题,"写一个根据id字段查找记录的缓存函数,如果之前查过,则直接返回之前查找过的对象,而无须重新查找"。当时由于时间较短加上时间比较紧张，考虑并不是特别全，并没有写出一个比较合适的方法（无法普及调用）。今天回过头想了一下，做了一些改进，望大家多给与指点。思路上采用闭包和数组的find方法。
var getItem=function () {
var cacheArr=[];
//判断数组是否支持find方法,如果不支持则扩充
if (!Array.prototype.find) {
Array.prototype.find = function(predicate) {
if (this === null) {
throw new TypeError('Array.prototype.find called on null or undefined');
}
if (typeof predicate !== 'function') {
throw new TypeError('predicate must be a function');
}
var list = Object(this);
var length = list.length >>> 0;
var thisArg = arguments[1];
var value;
for (var i = 0; i < length; i++) {
value = list[i];
if (predicate.call(thisArg, value, i, list)) {
return value;
}
}
return undefined;
};
}
getItemById= function(id,arr){
var temp=cacheArr.find(function (item) {return item.id==id})
if(temp==undefined){
var newItem=arr.find(function (item) {return item.id==id});
cacheArr.push(newItem);
console.log("New Data")
return newItem;
}else{
console.log("Cache Data")
return temp;
}
};
return getItemById;
}
Array.prototype.getItemById=function(id){
return getItem().call([],id,this);
}
测试对象及使用方法：
var scoresTable=[
{id:11,name:"小张",score:80},
{id:22,name:"小王",score:95},
{id:33,name:"小李",score:50},
{id:44,name:"小刘",score:65},
{id:55,name:"小徐",score:84}
] //模块初始化使用
console.log(scoresTable.getItemById(11))
console.log(getItemById(11,scoresTable)); //模块初始化使用
console.log(scoresTable.getItemById(22));
console.log(getItemById(11,scoresTable));
console.log(getItemById(22,scoresTable));
console.log(getItemById(11,scoresTable));
执行结果如下：
方案二：利用new方法处理。
function Cache(arr){
this.cacheArr=[];
this.arr=arr;
}
Cache.prototype.byId=function(id){
var temp=this.cacheArr.find(function (item) {return item.id==id})
if(temp==undefined){
var newItem=this.arr.find(function (item) {return item.id==id});
this.cacheArr.push(newItem);
console.log("New Data")
return newItem;
}else{
console.log("Cache Data")
return temp;
}
}
测试对象及使用方法：
var scoresTable=[
{id:11,name:"小张",score:80},
{id:22,name:"小王",score:95},
{id:33,name:"小李",score:50},
{id:44,name:"小刘",score:65},
{id:55,name:"小徐",score:84}
]
var data=new Cache(scoresTable);
console.log(data.byId(11));
console.log(data.byId(11));
console.log(data.byId(11));
console.log(data.byId(22));
console.log(data.byId(22));
执行结果如下：