How to type async RedisJSON methods correctly?

Question

I'm having an issue correctly typing the redis node package correctly. As an example of the base code for a simple JSON.GET

import * as redis from 'redis';
const client = redis.createClient();
async function getSomeData() {
    return await client.json.get('keyname', { path: '$.path'})
}

async functions return a Promise, and in this example, I expect the data returned from redis to be an array of objects, something like

type returnObject = {
  key1: string;
  key2: string;
}

What I'm struggling with is how to only return the first object from that returned array, if I try:

async function getSomeData() {
    return await client.json.get('keyname', { path: '$.path'})[0]
}

I get the following error in vscode:

Element implicitly has an 'any' type because expression of type '0' can't be used to index type 'Promise<string | number | boolean | Date | (string | number | boolean | Date | (string | number | boolean | Date | (string | number | boolean | Date | (string | ... 5 more ... | null)[] | { ...; } | null)[] | { ...; } | null)[] | { ...; } | null)[] | { ...; } | null>'.

and therefore, understandably, I get a similar error stating the same is not assignable to type returnObject if I try something like

async function getSomeData(): Promise<returnObject[]> {
    return await client.json.get('keyname', { path: '$.path'})
}

I think this type is coming from the RedisJSON type from the @node-redis package, but either way, I'm unclear on how to resolve this. The only way I can get close to something that works is to use a helper function that assigns the result of getSomeData to an any type, but that defeats the point of using TypeScript. Can anyone point me in the direction of how you should go about correctly typing async functions that use the new RedisJSON methods such that the results can be worked with? Thank you

Edit: for clarity, the package I'm using is https://www.npmjs.com/package/redis

Guy Royse · Accepted Answer · 2022-02-24 20:52:29Z

1

I believe your await is operating against the array access and not the call to client.json.get. I was able to get similar issue from JavaScript and resolved it by calling:

let results = await client.json.get('keyname', { path: '$.path'});
return results[0];

answered Feb 24, 2022 at 20:52

Guy Royse

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2 Comments

cb1210 Over a year ago

Thank you for your reply. Are you definitely using Typescript and the redis package I've referenced, as your example does not work for me. results[0] still has a similar error to the original one. results is of type string | number | boolean | .... | null and therefore I get the error saying that I cannot take the results[0] as results may be null. In a similar fashion I cannot set results to be returnObject[] as the return value from the json.get can be null

Guy Royse Over a year ago

I wasn't but I just tried it with TypeScript and see the same error. So not the most helpful answer! Interestingly, if I add a @ts-ignore to your code I get undefined as the result and if I wrap the await in parens, but not the [0] I get the string back.

H3AR7B3A7 · Accepted Answer · 2022-07-08 21:43:55Z

0

async function getSomeData(): Promise<returnObject[]> {
  return await client.json.get('keyname', { path: '$.path'}) as unknown as returnObject[]
}

Obviously you need to be sure that what you actually get from client.json.get(...) is of type Promise<returnObject[]> since this is essentially discarding the type of the return value and then casting it to what you want.

It's not the prettiest solution, but in my experience the typings in @redis/json aren't the greatest.

Hope this helps :)

edited Jul 8, 2022 at 21:43

H3AR7B3A7

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answered Jul 1, 2022 at 22:49

Cynicade

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