Node, Express, and parsing streamed JSON in endpoint without blocking thread

I'd like to provide an endpoint in my API to allow third-parties to send large batches of JSON data. I'm free to define the format of the JSON objects, but my initial thought is a simple array of objects:

{[{"id":1, "name":"Larry"}, {"id":2, "name":"Curly"}, {"id":3, "name":"Moe"}]}

As there could be any number of these objects in the array, I'd need to stream this data in, read each of these objects as they're streamed in, and persist them somewhere.

TL;DR: Stream a large array of JSON objects from the body of an Express POST request.

It's easy to get the most basic of examples out there working as all of them seem to demonstrate this idea using "fs" and working w/ the filesystem.

What I've been struggling with is the Express implementation of this. At this point, I think I've got this working using the "stream-json" package:

const express = require("express");
const router = express.Router();
const StreamArray = require("stream-json/streamers/StreamArray");

router.post("/filestream", (req, res, next) => {
    const stream = StreamArray.withParser();
    req.pipe(stream).on("data", ({key, value}) => {
        console.log(key, value);
    }).on("finish", () => {
        console.log("FINISH!");
    }).on("error", e => {
        console.log("Stream error :(");
    });
    res.status(200).send("Finished successfully!");
});

I end up with a proper readout of each object as it's parsed by stream-json. The problem seems to be with the thread getting blocked while the processing is happening. I can hit this once and immediately get the 200 response, but a second hit blocks the thread until the first batch finishes, while the second also begins.

Is there any way to do something like this w/o spawning a child process, or something like that? I'm unsure what to do with this, so that the endpoint can continue to receive requests while streaming/parsing the individual JSON objects.