In this article I would like to show you how you could use the @memoizeAsync decorator, from the utils-decorators library, in your application (both node and web) in one of the most elegant and simple ways.

Let’s say we have the following class:

export class SettingsProviderClient {
  getSettings(context): Promise<SettingsDto> {
    ...
  }
}

As you can see, the getSettings is returning a Promise of SeettingsDto. Now let’s say that we would like to have some caching which will check if a call was made in the last 10 minutes to getSettings with the same context then it would be pulled from the cache and won’t be resolved again.

First step, install the utils-decorators library:

npm install --save utils-decorators

Second step, apply the @memoizeAsync decorator:

import { memoizeAsync } from 'utils-decorators';
export class SettingsProviderClient {
  @memoizeAsync(1000 * 60 * 10) // 10 minutes in ms
  getSettings(context): Promise<SettingsDto> {
    ...
  }
}

That’s all! Now you have a 10 minutes cache.

Wait! there are more options

In the next few paragraphs we will discuss the @memoizeAsync API and it’s more advanced configurations.

Custom key resolving:
By default the decorator will put as the key of a cache entry the string which is generated by running JSON.stringify on the provided arguments to the decorated method. If you would like to change this behaviour then you will need to provide your own key resolver:

@memoizeAsync({
  keyResolver: (context) => context.id.toString(),
  expirationTimeMs: 1000 * 60 * 10
})
getSettings(context): Promise<SettingsDto> {
  ...
}

The cache attribute is expecting to receive an object that implements the Cache interface (which the JavaScriptMap object implements by default):

interface Cache<D> {
    set: (key: string, value: D) => void;
    get: (key: string) => D | null;
    delete: (key: string) => void;
    has: (key: string) => boolean;
}

Distributed cache:
In many cases you have more than one instance of your application running, in this cases you might want to have a distributed cache which all the instances of the application can share.
To achieve this you need to provide your custom cache which should implement the AsynCache interface

interface AsyncCache<D> {
    set: (key: string, value: D) => Promise<void>;
    get: (key: string) => Promise<D> | Promise<null>;
    delete: (key: string) => Promise<void>;
    has: (key: string) => Promise<boolean>;
}

The AsyncCache interface resembles the Cache interface but notice that every operation is async (returning a Promise).
For example, let’s say that we are using Redis (you can see a full implementation in this gist) as our distributed cache:

@memoizeAsync({
  keyResolver: (context) => context.id.toString(),
  expirationTimeMs: 1000 * 60 * 10,
  cache: redisCache
})
getSettings(context): Promise<SettingsDto> {
  ...
}

Different cache types for different environments
You probably noticed that both the local and the async caches are provided via the same cache attribute, so if we would like to use different caches for different environments we could achieve this with a simple condition check:

@memoizeAsync({
  keyResolver: (context) => context.id.toString(),
  expirationTimeMs: 1000 * 60 * 10,
  cache: isProd() ? redisCache : new Map()
})
getSettings(context): Promise<SettingsDto> {
  ...
}

Summery

Almost every production app has a cache, and dealing with a cache might be painful and inconvenient. IMO, by using a decorator this ordeal becomes much more pleasant, elegant and clear.

Previously published on Medium

How To Setup Caching in Nodejs

Wait! there are more options

Summery