How to run a command from a gnome extension

gnome-exec.js

/**
The first time I wanted to create an extension for Gnome, I spent two hours trying to understand how to do this, due to bad documentation.
So now I am sharing this once for all. 
*/
const ByteArray = imports.byteArray;
function exec(command) {
    const output = GLib.spawn_command_line_sync(command);
    return {
        ok: output[0],
        standard_output: ByteArray.toString(output[1]),
        standard_error: ByteArray.toString(output[2]),
        exit_status: output[3]
    }
}