coalescify

coalesce inflight promise calls into a single promise

import coalescify from 'coalescify';

const fetchResource = async (id: number) => {
  // ...
};

const coalescedFetchResource = coalescify(fetchResource);

const results = await Promise.all([
    coalescedFetchResource(1), 
    coalescedFetchResource(1),
    coalescedFetchResource(1),
    coalescedFetchResource(3)
])

// coalescedFetchResource(1) will only be called once, and the resolved result will be shared between all other calls
// coalescedFetchResource(3) will only be called once

coalescify will automatically determine inflight calls to coalesce based on the arguments passed to the function. If the arguments are the same, the promise will be shared.

a custom coalescion key generator function can be passed as the second argument

import coalescify from 'coalescify';

const fetchResource = async (type: string, id: number) => {
  // ...
};

const coalescedFetchResource = coalescify(fetchResource, (type, id) => `${type}/${id}`);

const results = await Promise.all([
    coalescedFetchResource('dog', 1), 
    coalescedFetchResource('dog', 1),
    coalescedFetchResource('dog', 2),
    coalescedFetchResource('cat', 1)
])

// coalescedFetchResource('dog', 1) will be called once
// coalescedFetchResource('dog', 2) will be called once
// coalescedFetchResource('cat', 1) will be called once

using a custom coalescion key generator is generally faster, since the default implementation uses JSON.stringify on function arguments, which is slower