gjs-signals-example.js

// see https://gitlab.gnome.org/GNOME/gjs/blob/master/doc/Modules.md#signals
const Signals = imports.signals;

class MyJSClass {
  testSignalEmission () {
    this.emit("example-signal", "moo", 42);
  }
}
Signals.addSignalMethods(MyJSClass.prototype);

const obj = new MyJSClass();
const handlerId = obj.connect("example-signal", (_obj, a, b) => {
  print("handler1", a, b);
});
obj.connect("example-signal", (_obj, a, b) => {
  print("handler2", a, b);
});

obj.testSignalEmission();
obj.disconnect(handlerId);

obj.testSignalEmission();
obj.disconnectAll();

$ gjs gjs-signals-example.js 
handler1 moo 42
handler2 moo 42
handler2 moo 42