reading and writing files in electron

client.js

const FILE_A = 'a.json'
const FILE_B = 'b.json'

const files = [FILE_A,FILE_B]
const contents = {}

window.api.receive("sendReadContent", (file_name,data) => {
    

    if (!files.includes(file_name)){
        throw "read file not in list"
    }
    
    contents[file_name] = data

    const read_files = Object.keys(contents)
    const all_is_read = files.every(a => {return read_files.includes(a)})

    if (all_is_read){
        do_stuff_after_all_read()
    }
})

function do_stuff_after_all_read(){
    console.log(contents)
}


window.api.send("askToRead", FILE_A)
window.api.send("askToRead", FILE_B)

const data_to_write = {important: "stuff to write"}
window.api.send("askToWrite", "to_write.json", JSON.stringify(data_to_write))

index.html

<script src="client.js"></script>

main.js

const {app,BrowserWindow,ipcMain} = require("electron");
const path = require("path");
const fs = require("fs");
  
let win;  
async function createWindow() {
	win = new BrowserWindow({
		width: 800,
		height: 600,
		webPreferences: {
			preload: path.join(__dirname, "preload.js")
		}
	})
	win.loadFile(path.join(__dirname, "public/index.html"));
}  
app.on("ready", createWindow);
  
ipcMain.on("askToRead", (event, file_name) => {
	fs.readFile(path.join(__dirname, file_name),'utf8', (error, data) => {
		win.webContents.send("sendReadContent", file_name, data);
	})
})

ipcMain.on("askToWrite", (event, file_name, contents) => {
	fs.writeFile(path.join(__dirname, file_name), contents, () => {});
})

preload.js

const {contextBridge,ipcRenderer} = require("electron");

contextBridge.exposeInMainWorld(
    "api", {
        send: (channel, ...args) => {
            // whitelist channels
            let validChannels = ["askToRead", "askToWrite"];
            if (validChannels.includes(channel)) {
                ipcRenderer.send(channel, ...args);
            }else {
                throw "invalid channel"
            }
        },
        receive: (channel, func) => {
            let validChannels = ["sendReadContent"];
            if (validChannels.includes(channel)) {
                // Deliberately strip event as it includes `sender` 
                ipcRenderer.on(channel, (event, ...args) => func(...args));
            }else {
                throw "invalid channel"
            }
        }
    }
)