Problems with setting up a small helloWorld

[Pixelherz23]

I try to recreate/understand the examples and wrote this typescript function, called in my main:

import { JSONSyncPreset  } from  "lowdb/node";

export function fooBar() {
    type Data = {
        messages: string[]
      }

      const message = 'HelloWorld'
      const defaultData: Data = { messages: [] }
      const db = JSONSyncPreset<Data>('file.json', defaultData)
      db.data.messages.push(message)

      db.write()
      console.log(db.read());

}

What I expect:

1. created file.json with data
2. console output with the db value

What I get:

1. file.json wont be created.
2. console.log prints undefined

PS: I dont understand the adpater LocalStoragePreset. When should I use it instead of the other adapters? Thx

[typicode]

It works on my side with the following code (I didn't use TS to test it quicker but it shouldn't have an impact):

❯ rm file.json 
❯ node index.mjs
undefined
❯ bat file.json 
───────┬────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: file.json
───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ {
   2   │   "messages": [
   3   │     "HelloWorld"
   4   │   ]
   5   │ }
───────┴────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
❯ bat index.mjs 
───────┬────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: index.mjs
───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ import { JSONSyncPreset } from "lowdb/node";
   2   │ 
   3   │ const message = 'HelloWorld'
   4   │ const defaultData = { messages: [] }
   5   │ const db = JSONSyncPreset('file.json', defaultData)
   6   │ db.data.messages.push(message)
   7   │ 
   8   │ db.write()
   9   │ console.log(db.read());
───────┴────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

/tmp/foo is 📦 v1.0.0 via  v21.2.0 
❯ 

So file.json is created. db.read() fills db.data it doesn't return a value. If you want to get log the content of the db, use console.log(db.data).

LocalStoragePreset is if you want to run lowdb in the browser, using window.localStorage.

I don't know why your code doesn't work though :thinking:

[Pixelherz23]

ok, db.data prints an array with the strings from previous tests I pushed in the DB. And I found the file.json. Its inD:\Users\xxx\AppData\Local\Programs\Microsoft VS Code. Weird.

db.read() fills db.data

I am quite confused now. I used the code above without .read(). I changed console.log(db.read()); to console.log(db.data ()); So how can it be that the db object has the data that is written in the file.json if I didnt used .read()?

Ps: You are awesome for answering so quickly. Most repos have so many questions on read. Thx <3

[typicode]

ok, db.data prints an array with the strings from previous tests I pushed in the DB. And I found the file.json. Its inD:\Users\xxx\AppData\Local\Programs\Microsoft VS Code. Weird.

You can use an absolute path to ensure that file.json is where you expect it to be. You can make it relative to your source file (https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c#what-do-i-use-instead-of-__dirname-and-__filename).

So how can it be that the db object has the data that is written in the file.json if I didnt used .read()?

It's not mentioned in the docs, so I understand the confusion. Presets automatically read the database so that can start using data directly.

https://github.com/typicode/lowdb/blob/main/src/presets/node.ts#L29

PS: thank you :bow: but unfortunately I have many questions that are left unanswered because of time/lack of funding ^^' so to be honest here it's a bit of luck ;)