Godot Signals & Groups (4.x)

Decouple nodes with the observer pattern (signals) and act on many nodes at once (groups), instead of hard-coding references between scenes. Targets Godot 4.7.

When to use

• Use when a node needs to tell others "something happened" (player died, item picked up, wave cleared) without holding direct references to them.
• Use when you need to address a whole category of nodes at once ("pause all enemies", "save every checkpoint").

When not to use: raw signal syntax basics → godot-gdscript; scene structure and instancing → godot-nodes-scenes. For cross-scene global events, emit from an autoload (see godot-nodes-scenes).

Core workflow

1. Decide the direction. A child/sub-scene should emit a signal upward; the parent connects to it. This keeps the child reusable and ignorant of who listens.
2. Declare typed signals on the emitter; emit() them when the event occurs.
3. Connect with a Callable (sig.connect(_on_sig)), optionally in the editor's Node dock. Use CONNECT_ONE_SHOT for fire-once, bind() to pass extra context.
4. Use groups for broadcast: add nodes to a named group, then iterate get_tree().get_nodes_in_group(...) or call_group(...).
5. Disconnect when needed (e.g. before freeing a long-lived listener) and check is_connected() to avoid duplicate connections.

Patterns

1. Emit upward, connect from the parent

# coin.gd (reusable pickup, knows nothing about the player or HUD)
extends Area2D
signal collected(value: int)

func _on_body_entered(body: Node) -> void:
    if body.is_in_group("player"):
        collected.emit(10)
        queue_free()

# level.gd (the parent wires the coin to game state)
func _ready() -> void:
    for coin in get_tree().get_nodes_in_group("coins"):
        coin.collected.connect(_on_coin_collected)

func _on_coin_collected(value: int) -> void:
    GameState.add_score(value)