JavaScript: how to add data to an array inside JSON file

Question

I'm trying to build a simple Discord.js bot, but I'm having trouble adding user input to an array stored within a json file.

I'd like to have a single json file that will store information the bot can draw on, including an array of quotes that is also able to be added to by users. Currently, the settings.json file looks like this:

{ "token" : , //connection token here

  "prefix" : "|", //the prefix within messages that identifies a command

  "quotes" : [] //array storing a range of quotes
}

I can then draw information from the array, choosing a random quote from those currently stored, as shown below:

const config = require("./settings.json");

var quotes = config.quotes;

function randomQuote() {
    return quotes[Math.floor(Math.random() * quotes.length)];
};


if(message.content.toLowerCase() === prefix + "quote") {

    message.channel.send(randomQuote());

}

This all works as intended, but I can't for the life of me work out how to allow users to add a quote to the array (it'd use a command something like |addquote). I know that, for writing data to a json file, I'd use something like this:

var fs = require('fs');

let test = JSON.parse(fs.readFileSync("./test.json", "utf8"));

if(message.content.toLowerCase() === 'test') {

    test++;

    fs.writeFile("./test.json", JSON.stringify(test), (err) => {
        if (err) console.error(err)
    });

}

But what for what I'm trying to do now - target a specific array within an existing json file that contains other data separate to the array, and add a new entry rather than overwrite what's there - I'm pretty much stumped. I've looked around a lot, but either I haven't found what I'm looking for, or I couldn't understand it when I found it. Could anyone help me out here?

shalvah · Accepted Answer · 2018-03-16 14:20:57Z

2

Push the new item into the array:

config.quotes.push(newQuote);

Edit: I should point out that using require to read a JSON file this way would likely cache it, so changes you make to the file might not show up the next time you require it.

edited Mar 16, 2018 at 14:20

answered Mar 16, 2018 at 14:11

shalvah

89510 silver badges23 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Gala Pagois Over a year ago

Well now I feel like a complete idiot. Thanks very much for pointing out the obvious for me! Also, in regards to require, I'm looking at using JSON.parse(fs.readFileSync("./settings.json", "utf8")); instead, would that work better?

shalvah Over a year ago

Lol... We all have days like that. Your suggestion would work. Better is subjective, because you're doing blocking I/O (generally frowned upon). Did you verify the caching? That is, require the JSON file, push to the array, write back to the file, and then require again and check if the changes are reflected?

Jason Cust · Accepted Answer · 2018-03-16 14:21:07Z

0

A file can't be "edited" aside from concatenation at the end of the file. To modify the file outside of that would require to do so in memory and then overwrite the existing file with the value in memory. That said there are many concerns with using a file like this for storing user input, some of which include: limiting the size of the file; multiple processes possibly reading from the same file that can be overwritten by any one of them; a process crash or an error during a write that would render the file useless; etc.

Have you looked into a real data store? Any simple DB would work and this is actually what they are made for.

answered Mar 16, 2018 at 14:21

Jason Cust

10.9k2 gold badges36 silver badges45 bronze badges

1 Comment

Gala Pagois Over a year ago

I intend to further down the line, but I'm still trying to get to grips with the basic stuff here, so I feel like that might be a little ways beyond my reach right now. If you've got any advice on where to look for info on it, though, I'd be grateful!

Collectives™ on Stack Overflow

JavaScript: how to add data to an array inside JSON file

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related