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cachy

Cachy adds a caching layer to your javascript clients. It is designed to add your own storages (plain objects, local storage and more), clients (like axios, fetch and more) and caching strategies.

Tutorial

Code can be found in public.

Let´s assume following project: We want to create a simple app where we can fetch github user data. As we just want to fetch some basic data that won´t change very fast, we want to cache the results in a very simple way.

As a result we want following things

• caching get calls
• storing response in local storage
• after performing a request it should get stored for 60 seconds. After that time the response should be renewed
• using window.fetch

Cachy doesn´t provide that requirements out of the box (there will be implemtations in the future for storage, caching and co.) but the library provides useful interfaces, classes and methods that will help you to create it by your own. Plus: you can change caching strategies and storage later without rewriting everything.

Following the requirements we need to do:

• creating our Client class that redirects requests between Cachy and window.fetch
• creating our Cache class that handles the caching logic
• creating our Storage class that will store responses into the local storage
• setup up Cachy

Creating our client

As mentioned before we want to use window.fetch. Therefore we need a class that implements the interface Client. Let´s create our class FetchClient in file public/fetch-client.ts.

import { Client } from '../lib';

class FetchClient implements Client {
    
};

export default FetchClient;

For now we get a typescript error because we didnt implement the request method yet. This method will get the Request object as an argument and should return a promise. So lets create our request method. In our simple app we just need the method and the url. In other cases when we need to pass data as a request-body or request-header we need data.

import { Client, Request } from '../lib';

class FetchClient implements Client {
    async request(requestData: Request): Promise<any> {
        if (requestData.method === 'get') {
            const response = await fetch(requestData.url);
            const data = await response.json();
            return data;
        }
    }
};

export default FetchClient;

Creating our storage

Our storage interface is quite simple. We need to create a class that implements a read and write method. Both methods become id: Id and item: CacheItem as an argument. Let´s create our class.

import { Storage, CacheItem } from "../lib";

class LocalStorage implements Storage {
    async read({ id }: { id: string }): Promise<any> {
        const result = localStorage.getItem(id);

        if (result === null) {
            return false;
        }

        return JSON.parse(result);

    };
    async write({ id, item }: { id: string; item: CacheItem; }): Promise<boolean> {
        try {
            localStorage.setItem(id, JSON.stringify(item))
            return true;
        } catch (error) {
            console.error(error);
            return false;
        }
    }
};

export default LocalStorage;

Creating our cache handler

Last but no least we need to create our caching class. In this class we need to implement our caching logic. For our example we want to check if there is an excisting cache item with the correct request id and them look if that request is older then seconds.

Therefore we need to dynamical add infos to our reqest object. Request.info is the place where you can write and read data for those cases.

import { Cache, CacheItem, Request } from '../lib';
import { Response } from '../lib/types.d';

class TimeCache extends Cache {
    constructor({ storage}) {
        super({ storage });
    }

    async handle({ id, request, response }: { id: string, request: Request, response: Response }): Promise<any> {
        // response will be passed if 
        if (response) {
            const currentTimestamp = Date.now();

            // inject timestamp into request object
            request.info = {
                lastUpdate: currentTimestamp,
            };

            const item = new CacheItem({
                request,
                response,
            });

            await this.write({ id, item });
            return item;
        }

        const item = await this.read({ id });
        const noItemInCache = item === false;

        if (noItemInCache) {
            return false;
        }

        const lastUpdate = item.request.info.lastUpdate;
        const currentTimestamp = Date.now();

        const shouldRefreshRequest = (currentTimestamp - lastUpdate) > 60 * 1000;

        if (shouldRefreshRequest) {
            return false;
        }

        return item;
    }
}

export default TimeCache;

Setup Cachy and dom interaction

import { Cachy } from '../lib';
import FetchClient from './fetch-client';
import LocalStorage from './local-storage'; 
import TimeCache from './time-cache';

const url = (username: string) => `https://api.github.com/users/${username}`;

const storage = new LocalStorage();
const cache = new TimeCache({ storage });
const client = new FetchClient();

const apiClient = new Cachy({
    cache,
    client,
});


const elements = {
    bio: document.querySelector('.user-info__bio'),
    location: document.querySelector('.user-info__location'),
    input: document.querySelector('.user-form__input'),
    button: document.querySelector('.user-form__button')
};

elements.button.addEventListener('click', async () => {
    const result = await apiClient.request({ url: url(elements.input.value), method: 'get' });
    elements.bio.textContent = result.response.bio;
    elements.location.textContent = result.response.location;
});

HTML code is in the public/index.html. When you enter a github username we fetch the data from github api. As you can see in the network panel: After the first request, every following click will get the result from cache. Afer 60 seconds it will refetch the data from the api.

Every request needs an ID. By default the ID is based on the url and method.

If you need to create special ID based on the request. You can pass a custom function to the Cachy.options object.

In our example we want to fetch user data. This could be an ID for post request that get user data from a specific user. The user would be passed into the body e.g. https://nice-users.com/user {data: 'jan'}.

const apiClient = new Cachy({
    cache,
    client,
    options: {
        generateId(request) {
            return `${request.url}-${request.data.user}`
        }
    }
});

API

Implementations

Design

classDiagram
    class Storage
    <<interface>> Storage
    Storage: read()
    Storage: write()
    
    class Cache
    <<abstract>> Cache
    Cache: -Storage storage
    Cache: handle()
    Cache: write()
    Cache: read()

    Cache --> Storage
    
    class Client
    <<interface>> Client

    class Cachy
    Cachy: -Cache cache
    Cachy: -Client client
    Cachy *-- Cache
    Cachy *-- Client