Simple-data-loader NPM

simple-data-loader

Introduction

simple-data-loader lets you cache a function's return value as a promise. It supports simple cache invalidation via timeouts in a minimal and dependency-free manner. It supports multi-argument functions and non-primitive arguments, and can be used for rate limiting.

simple-data-loader is heavily inspired by facebooks dataloader package and its api. However unlike facebooks dataloader, it places no emphasis on batching and as such allows for greater flexibility in selecting a loading function specific to your use-case.

It is designed to be simple, noise-free, have no external dependencies, and overall easy to use.

Installing

npm install simple-data-loader --save

Examples

caching resources

const dataloader = require('simple-data-loader');

function getResource(id) {
  // your implementation
}

const resouceLoader = dataloader(getResource, { ttl: 5000 });

const resourcePromise = resourceLoader('resourceID');

// await or the handle promise as you will.
// However resulted promise is cached for key `resourceID` for the next 5000 milliseconds

// If however you want to invalidate a key programitically you can:
resourceLoader.delete('resourceId');
resourceLoader('resourceId'); // will generate a new request for the underlying resource and cache it.

simple-data-loader can also be used to cache functions that have multiple arguments. This does not however mean that it can cache functions of variable arguments. It is only compatible with invocations with the same or less number of arguments as the function signature.

Setting a ttl (time to live) in the options works as in the previous example.

const dataloader = require('simple-data-loader');

function getBook(title, language, year) {
  // your implemenation
}

const bookLoader = dataloader(getBook);

const bookPromise1 = bookLoader('the old man and the sea', 'en', 1951);
const bookPromise2 = bookLoader('the old man and the sea', 'en', 1951);

bookPromise1 === bookPromise2; // true

bookLoader.delete('the old man and the sea', 'en', 1951);

const bookPromise3 = bookLoader('the old man and the sea', 'en', 1951);

bookPromise1 === bookPromise3; // false

Optionally one can choose to pass the loader function as part of the options object. The following code creates a loader with a timeout of 1 second.

const dataloader = require('simple-data-loader');

const myLoader = dataloader({
  load: () => {
    /*...*/
  },
  ttl: 1000,
});

By default simple-data-loader will not hash non-primitive types. This can be changed by setting the hash option to true. Fair warning the hash function is a simple deterministic version of JSON.stringify therefore caching using large objects or function definitions as arguments can be memory and computationally intensive. Use carefully.

For simple cases with functions that use option style objects this can be quite useful.

WARNING Circular objects will cause an infinite loop and eat all memory until the process crashes. Use hashing with care.

const dataloader = require('simple-data-loader');

function getListOfBooks(query, opts) {
  // your implementation
}

const loader = dataloader(getListOfBooks);

const promise1 = loader('hemingway', { limit: 5, sortBy: 'title' });
const promise2 = loader('hemingway', { limit: 5, sortBy: 'title' });

promise1 === promise2; // false, since although equal the two option objects are not the same reference

const hashLoader = dataloader(getListOfBooks, { hash: true });

const promise3 = loader('hemingway', { sortBy: 'name', limit: 5 });
const promise4 = loader('hemingway', { limit: 5, sortBy: 'name' });

promise3 === promise4; // true, the options objects needs only be equal. Key ordering does not matter

The max option can be passed to set a limit on the number of items that you want to cache. If a limit is set items will be evicted using the least recently used principle.

const dataloader = require('simple-data-loader');

const loader = dataloader(x => x, { max: 3 });
loader(1);
const promise2 = loader(2);
loader(1);
loader(3);
loader(4); // At this point "2" shall be evicted from the cache as it was the least recently used
const anotherPromise2 = loader(2);

promise2 === anotherPromise2; // false, this is not the same promise.

Supported options:

load (function => the loading function)
ttl (number => the time to live for cached items, if not provided will cache indefinitely unless programatically removed)
hash (boolean => enables hashing ie. a determinstic Stringify, and allows for non primitive type arguments)