Linux get notification on focused gui window change

Question

In linux, is it possible to get notifications when the currently focused GUI app changes? I\'m writing an app that tracks how long a user stays on each GUI app(per process, not

Answer 1

Example in JavaScript using node-x11:

var x11 = require('x11');
x11.createClient(function(err, display) {
  var X = display.client;
  X.ChangeWindowAttributes(display.screen[0].root, { eventMask: x11.eventMask.PropertyChange });
  X.on('event', function(ev) {
    if(ev.name == 'PropertyNotify') {
      X.GetAtomName(ev.atom, function(err, name) {
        if (name == '_NET_ACTIVE_WINDOW') {
          X.GetProperty(0, ev.window, ev.atom, X.atoms.WINDOW, 0, 4, function(err, prop) {
            console.log('New active window:' + prop.data.readUInt32LE(0));
          });
        }
      });
    }
  });
});