Electron Method Callback - node.js

Question

I'm new to electron and trying to build an application to control smarthome-components from my Mac. To do this, I need many HTTP-Request so the idea is to make an own method/function for this job.
Now my problem is, that I don't know how to use this callback-thing ;)
This is my code now:
const {app, Tray, Menu, BrowserWindow, net} = require('electron');
const path = require('path');
const iconPath = path.join(__dirname, 'icon.png');
let appIcon = null;
let win = null;
var http = require('http');
function httpGet(url, callback) {
http.get(url, (res) => {
const { statusCode } = res;
const contentType = res.headers['content-type'];
res.setEncoding('utf8');
let rawData = '';
res.on('data', (chunk) => { rawData += chunk; });
res.on('end', () => {
return callback(rawData);
});
}).on('error', (e) => {
console.error(`Got error: ${e.message}`);
});
}
app.on('ready', function(){
win = new BrowserWindow({show: false});
appIcon = new Tray(iconPath);
var contextMenu = Menu.buildFromTemplate([
{
label: 'http',
click: function() {
console.log(httpGet('http://192.168.178.10/switches/status_1'),
function(result) {
console.log(result);
}
);
}
}
]);
appIcon.setToolTip('This is my application.');
appIcon.setContextMenu(contextMenu);
});
Trey works, but the httpGet function does not return anything (undefined [function]) and electron crashes.
Would be really thankful if someone could help me with this.
Greetings,
Lukas

Answer 1

Bad news is that I do not know electron, so the TL;DR for the text below is as simple as: put a console.log line into the callback passed to http.get.
There is no return value in httpGet (and it is normal), that is why you can not log it. JavaScript event handling works with callbacks, and getting data via HTTP is an event.
What you have as second argument for http.get is the event handler.
While now it appears as a fancy lambda,
(res)=>{...}
in oldschool way it would look like
function(res){...}
So that is a function, and it will get invoked when something happens to the HTTP request you have issued, and that is where you could log/dig into the result (res).
What you see in your log at the moment:
undefined is the return value of a function which does not return anything, httpGet
[function] is the function you pass as second argument for console.log
function a(){} // a function which does not return anything
console.log(a(),a); // logs function result and function itself

Answer 2

First of all, the callback pattern is usually to write a function that accepts 2 parameters: err and result. If there was no error err becomes null, if there was an error result becomes null. So this would be the best way to write httpGet:
function httpGet(url, callback) {
http.get(url, (res) => {
const {
statusCode
} = res;
const contentType = res.headers['content-type'];
res.setEncoding('utf8');
let rawData = '';
res.on('data', (chunk) => {
rawData += chunk;
});
res.on('end', () => {
return callback(null, rawData);
});
}).on('error', (e) => {
console.error(`Got error: ${e.message}`);
return callback(e, null)
});
}
Second, the way you wrote your call to httpGet is wrong. Change this:
console.log(httpGet('http://192.168.178.10/switches/status_1'),
function(result) {
console.log(result);
}
);
To
httpGet('http://192.168.178.10/switches/status_1', function(err, rawData) {
if (err) {
console.error('httpGet failed!');
} else {
console.log(rawData)
}
});