Why, after running json-concat, the output contains the contents of only one json, and not all jsons in the folder?

Question

JSON

Hello!

I want to stitch all json's in a folder. Just objects next to each other.
Made a folder with test objects a.json, b.json and c.json with the same structure. Here is the start of a.json:

[
 {
   "header": "a1",
   "date": "a2",
   "body": "a3",
   "link": "a4"
 },
 {
   "header": "b1",
   "date": "b2",
   "body": "b3",
   "link": "b4"
 },

In b.json, everything is done the same, but the letters of the alphabet are double. In c.json - triple I run

the following most primitive script in the folder with these objects, almost a copy-paste from the documentation:

var jsonConcat = require("json-concat");
 
jsonConcat({
  src: "./Testjoin/",
    dest: "./Testjoin/result.json"
}, function (json) {
    console.log('done');
});

I'll never know - for some reason, in the output json'e there are no stitched objects, but only c.json content, for example. Or b.json. Obviously - the one that went to the script last.

I want to get sequentially stitched (the order is not important) the contents of a, b and c

Tell me where to dig?
Thank you!