Electron function to read a local file - FS - Not reading

Basically you need to do the following things.

1.Loading required dependencies

var remote = require('remote'); // Load remote compnent that contains the dialog dependency
var dialog = remote.require('dialog'); // Load the dialogs component of the OS
var fs = require('fs'); // Load the File System to execute our common tasks (CRUD)

2.Read file content

dialog.showOpenDialog((fileNames) => {
    // fileNames is an array that contains all the selected
    if(fileNames === undefined){
        console.log("No file selected");
        return;
    }

    fs.readFile(filepath, 'utf-8', (err, data) => {
        if(err){
            alert("An error ocurred reading the file :" + err.message);
            return;
        }

        // Change how to handle the file content
        console.log("The file content is : " + data);
    });
});

3.Update existing file content

 var filepath = "C:/Previous-filepath/existinfile.txt";// you need to save the filepath when you open the file to update without use the filechooser dialog againg
var content = "This is the new content of the file";

fs.writeFile(filepath, content, (err) => {
    if (err) {
        alert("An error ocurred updating the file" + err.message);
        console.log(err);
        return;
    }

    alert("The file has been succesfully saved");
});

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One more thing to add..Please check that your path to file is correct. You could do something similar to below.

var path = require('path');
var p = path.join(__dirname, '.', 'README.md');

Just one update information for the accepted answer. After the update of electron, you can directly use

const { dialog } = require('electron');

to import dialog.

And for remote, if you need to use it, you also need:

const { remote } = require('electron');

https://www.electronjs.org/docs/latest/api/dialog/