Signals are similar to calling methods, you can call them.
signal random_signal(some_vec: Vector2i)
$g.example_obj.random_signal([4,5])
You can connect to gdscript signals from javascript:
$g.example_obj.random_signal.connect((res) => {
// will print the vector2i as a javascript array with 2 elements: [x,y]
console.log("signal from godot: ", res);
});