记忆函数的性能优化

求阶乘

一般求阶乘的方法

function factorial(n) {
    
    if (n == 0 || n == 1) return 1;
    return n * factorial(n - 1)
}
console.time("factorial");
factorial(3000)
console.timeEnd("factorial");

可以看到直接运行时间大概在0.3s左右

通过hash表来进行缓存

let cache = {
    };
function getCache(n) {
    
   if (cache[n]) return cache[n];
   if (n == 0 || n == 1) return (cache[n] = 1);
   return (cache[n] = n * getCache(n - 1));
}
   console.time("getCache-first");
   getCache(3000)
   console.timeEnd("getCache-first");


   console.time("getCache-second");
   getCache(2000)
   console.timeEnd("getCache-second");

可以发现第一次调用时0.9s 第二次调用就是0.01s

高阶记忆函数

将该过程进行抽象化成一个函数让其拥有通用性

function memorize(fn) {
    
    let cache = {
    };
    return function () {
    
        let key = fn.name + '_' + [].join.call(arguments, ','); //函数名和参数进行拼接
        // console.log(key, arguments);
        return (cache[key] = cache[key] || fn.apply(this, arguments));
    }
}

let memorizeFactory = memorize(factorial);

console.time("memorizeFactory-first");
memorizeFactory(3000)
console.timeEnd("memorizeFactory-first");


console.time("memorizeFactory-second");
memorizeFactory(3000)
console.timeEnd("memorizeFactory-second");

实现缓存

import {
    api} form "./utils";
const cache  = {
    };
const request = async (url) => {
    
    if(cache[url]){
    
        return cache[url]
    }
    const response = await api(url);
    cache[url] = response;
    return response
}