Kevin Powell - Community•2y ago

NodeJS app.js requiring a JSON file?

I know that if I had some JSON data in a .js file, that I could, at the end of that .js file, do a module.exports() of that JSON module's name, and then require it in my app.js, and use a res.json() on it. (pics 1-3) But what if instead of having that JSON data in a js file, it was housed in its own .json file? I couldn't do a module.exports() from inside a .json file. Simply requiring the file inside of app.js and using the same res.json() on it doesn't work. Are we meant with NodeJS to just convert any JSON files to .js first if we intend to use it in app.js, in order to get access to it?

9 Replies

13eck•2y ago

If you want to read a .json file you'll need to use the fs module to read the file, then parse it as a JSON string into a JS object. As an example (note I'm using ES6 import syntax instead of CJS require() syntax):

import { readFile } from 'node:fs/promises';

const getFile = async (filename) => {
  const filePath = new URL(`./{filename}`, import.meta.url);
  const contents = await readFile(filePath, { encoding: 'utf8' });
  let obj;
  try {
    obj = JSON.parse(contents);
    return obj;
  } catch (e) {
    throw new Error(e)
  }
}

import { readFile } from 'node:fs/promises';

const getFile = async (filename) => {
  const filePath = new URL(`./{filename}`, import.meta.url);
  const contents = await readFile(filePath, { encoding: 'utf8' });
  let obj;
  try {
    obj = JSON.parse(contents);
    return obj;
  } catch (e) {
    throw new Error(e)
  }
}

https://nodejs.org/dist/latest-v18.x/docs/api/fs.html#fspromisesreadfilepath-options

thethingisbackOP•2y ago

Okay and then what would I need to do in order to get it to appear on the page when '/' is loaded? Do I need to send it to a file first?

13eck•2y ago

You can’t send a JS object over the wire. You’ll need to send the JSON file as a string and parse it on the front-end. Or, even better, let your reverse proxy handle the file system and your app should only handle the business logic. Caddy, nginx, et al are going to be much better at sending files than Node ever will. That’s what they do.

thethingisbackOP•2y ago

what does sending something "over the wire" mean? are you saying there's no way to have the express server directly take in a .json file's information, such that it's usable?

13eck•2y ago

JavaScript objects are a construct of the language and can’t be transmitted outside of the local environment. That means you can’t send them from the backend to the front end, that’s why there’s the JSON spec: to serialized a language-specific construct into something that can be sent via HTTP And no, I’m no saying that. I saying that you can’t send an object via HTTP. What you’re trying to do here is send a file, no use the info. So send the file and let your front end parse and use the JSON

Unknown User•2y ago

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13eck•2y ago

That's for serializing and sending a JS object, not for reading a JSON file and sending it What the OP is asking for is to read and send a file, not a JS object. Interacting with the file system is usually better left to the reverse proxy set up while the API is passed through to the back end. There's little reason to have the back end read the file and send it when that's what the reverse proxy is desined to do. Best tool for the job and everything

Unknown User•2y ago

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13eck•2y ago

You're still not sending a JS object, you're sending a stringified interpretation of it Since JSON is a string, you can omit the res.json() and just res.send() or whatever Express uses to send string data

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NodeJS app.js requiring a JSON file?