Promise.all and Promise.allSettled have made it easy to run promises parallelly. However, the data returned by Promise.allSettled (which is what I often end up having to use because Promise.all fails at the first promise that rejects/fails) is slightly cumbersome to deal with.
Instead, I use a recipe where it becomes easy for me to run parallel promise functions and handle the data far more easily.
Before I show the recipe, here's how the usage looks like:
// let's say we have these functions that return a promise
const getUsers = () => axios.get('/users');
const getTeams = () => axios.get('/teams');
const getPlans = () => axios.get('/plans');
const setConfig = () => axios.post('/config', { data: config }); // config comes from somewhere
// now, we have to run these on app-load
const results = await runPromises({
users: getUsers,
teams: getTeams,
plans: getPlans,
config: setConfig,
});
// runPromises is the recipe.
// and then `results` will look like this:
// results == {
// users: { data: [...] }, // or { error: AxiosError }
// teams: { data: [...] }, // or { error: AxiosError }
// plans: { data: [...] }, // or { error: AxiosError }
// config: { data: {...} }, // or { error: AxiosError }
// }
The object-based approach is not as great as a list but you can see the benefit - no need to deal with status and value and reason for each. Instead, each key in your object (which maps to a function) will have a resolved value object that either contains the data key or the error key.
Here's the recipe to use:
const runPromises = async (promises) => {
let plist = Object.entries(promises).map(async ([name, promise]) => {
let res;
try {
res = { data: await promise() };
} catch (e) {
res = { error: e };
}
return [name, res];
});
let intermediateResult = [];
for (let p of plist) {
await intermediateResult.push(await p);
}
return Object.fromEntries(intermediateResult);
};
Briefly, what we do is convert the object into a [key, value] pair list, then run each promise (but because this is a map, it is run parallelly), and finally collect these promises into another [key, value] pair list and return that as an object.
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