ES6 import of JSON returns 'undefined'

Question

When I want to import JSON into my Node application following es6 like this:

import * as config from "./server-config.json" assert {type: 'json'}

When I try to use the imported values like this

console.log(config["url"])

It will just return the value undefined. I am having this problem using Node 19, the path is correct, the json is correct and even if I use --experimental-json-modules it will return an undefined.

"Experimental" means "might not work". Why is it so critical that you *import* the file? Just use fs.readFileSync and JSON.parse the contents. — Jared Smith, Jan 17 '23 at 17:21
Related: [Import '.json' extension in ES6 Node.js throws an error](/a/60206393/4642212). — Sebastian Simon, Jan 17 '23 at 19:17

Thomas Sablik · Accepted Answer · 2023-01-17T19:12:17.880

A JSON module is equivalent to an ES6 module with default export.

The line

import * as config from "./server-config.json" assert {type: 'json'}

imports the JSON module into config.default. You can either log it with

console.log(config.default["url"])

or import the default export with

import config from "./server-config.json" assert {type: 'json'}

and log with

console.log(config["url"])

More info about JSON import: https://v8.dev/features/import-assertions

score -2 · Answer 2 · answered Jan 17 '23 at 18:09

-2

If there were several functions/objects/arrays/consts were exported in one file and you wanted to import them all as a single object in that case import * as everything from "./moduleLocation" would be correct.

In your case, there is a single JSON object in the server-config.json file located in the project root. Therefore, it would be appropriate to import that JSON object, if it was exported, as a single object.

import config from "./server-config.json";

In order to be able to read that JSON object data you will need to parse it to the object:

const serverConfigs = JSON.parse(config);

Now you can read/access everything from serverConfigs;

answered Jan 17 '23 at 18:09

jkalandarov

564
5
15

1

You have to parse strings. `import` won't import `config` as a string. – Thomas Sablik Jan 17 '23 at 18:11
Again: `config` won't be a string. You can't parse it. You can only parse strings. – Thomas Sablik Jan 17 '23 at 18:16
`config["url"]` being `undefined` is pretty clear. – jkalandarov Jan 17 '23 at 18:21
3

https://v8.dev/features/import-assertions The import imports an object, not a JSON string. – Thomas Sablik Jan 17 '23 at 18:27
@jkalandarov I think you should test this code and see that it wont work.. you can't use ESM syntax to import a json file without asserting the type as json – about14sheep Jan 17 '23 at 18:34

ES6 import of JSON returns 'undefined'

2 Answers2