JavaScript编写一个缓存功能的功能（记忆）

Question

I have been asked this question and I wasn't sure how I can target this.

Question:

Write a cache function which caches a function and returns a result if it was already executed in the past.

Let's say if there's a function Fibonacci(20) = 6765

cacheFunction(Fibonacci(20)) // it should not execute the function instead return 6765. 

But if i give cacheFunction(Fibonacci(21)) //It's not cached, execute the function

My attempt:

function cacheFunction(funct) {

    var obj = {};

    if (obj.hasOwnProperty(funct)) { //checking if the argument is in the object?
        return obj[funct];
    } else { //if not present, then execute the function, store it in cache and return the value.
        obj[funct];
        return funct;
    }
}

But I'm not able to understand how to get the arguments in one function inside another function? (The person told me that I need to use closure to get it)

Can someone enlighten me?

Answer 1

It's not cacheFunction(Fibonacci(20)) , it's cacheFunction(Fibonacci)(20) . You indeed cannot get the parameters of Fibonacci , you cannot alter that function to somehow access them. What cacheFunction is supposed to do is to construct a new function that provides the same functionality as the passed-in funct (ie Fibonacci in your case) by wrapping around it. In the wrapper function that will eventually get called with the input (eg 20 ) you can access the arguments and check the cache for their values, and potentially pass them on to funct .

Answer 2

Memoization/caching technique is available as part of underscore.js. You can directly use it if needed. I also added a sitepoint article which walks you through implementing memoization in JS.

Implementing Memoization in JavaScript

memoize in underscorejs