Processing a JSON file using JSONata in Node.JS returns undefined

Question

Processing a JSON file using JSONata in Node.JS returns undefined. Why is this happening?

I tried this but it's returning "undefined"

index.js

    const jsonata = require("jsonata");
    const fs = require("fs");

    (async () => {
        const json = fs.readFileSync("test.json", {encoding:'utf8', flag:'r'});
        const expression = jsonata('V1.fields');
        const result = await expression.evaluate(json);
        console.log(result);
    })()

test.json

[
  12345,
  {
    "V1": {
      "fields": {
          "id": 0
      }
    }
  }
]

output

% node index.js  
undefined

https://try.jsonata.org/N02gm7EYz

Answer 1

Despite its name, jsonata doesn't evaluate JSONs, it evaluates objects. You need to parse the JSON being read before passing it to jsonata.

You could do this explicitly:

const json = JSON.parse(fs.readFileSync("test.json", {encoding:'utf8', flag:'r'}));

But to be honest, it's easier to just require it and let Node.js do the "heavy" lifting:

const json = require("./test.json");