Signals are now classes. For easier typing.

src/Signal.ts

@@ -1,26 +1,22 @@
-export function Signal<Payload extends any = void>() {
-  type Listener = (payload: Payload) => void
+export class Signal<Payload = void, Listener extends Function = (payload: Payload) => void> {
+  private listeners = new Array<Listener>()
 
-  const listeners = new Array<Listener>()
-
-  function add(fn: Listener) {
-    listeners.push(fn)
+  add(fn: Listener) {
+    this.listeners.push(fn)
   }
 
-  function remove(fn: Listener) {
-    const pos = listeners.indexOf(fn, 0)
-    if (pos > -1) listeners.splice(pos, 1)
+  remove(fn: Listener) {
+    const pos = this.listeners.indexOf(fn, 0)
+    if (pos > -1) this.listeners.splice(pos, 1)
   }
 
-  function clear() {
-    listeners.length = 0
+  clear() {
+    this.listeners.length = 0
   }
 
-  function emit(payload: Payload) {
-    for (const listener of listeners) {
+  emit(payload: Payload) {
+    for (const listener of this.listeners) {
       listener(payload)
     }
   }
-
-  return { add, remove, clear, emit }
 }

test/Signal.test.ts

@@ -4,7 +4,7 @@ describe("Signal", () => {
   it("provides a signal that listeners can be added to which are then called back once the signal is invoked", () => {
     let proof = ""
 
-    const signal = Signal<string>()
+    const signal = new Signal<string>()
     signal.add((payload) => (proof = payload))
     signal.emit("it works")
 
@@ -16,7 +16,7 @@ describe("Signal", () => {
       let proof = ""
       const listener = (payload: string) => (proof = payload)
 
-      const signal = Signal<string>()
+      const signal = new Signal<string>()
       signal.add(listener)
       signal.emit("it works")
       expect(proof).toEqual("it works")
@@ -32,7 +32,7 @@ describe("Signal", () => {
       let proof = ""
       const listener = (payload: string) => (proof = payload)
 
-      const signal = Signal<string>()
+      const signal = new Signal<string>()
       signal.add(listener)
       signal.emit("it works")
       expect(proof).toEqual("it works")
@@ -42,4 +42,12 @@ describe("Signal", () => {
       expect(proof).toEqual("it works")
     })
   })
+
+  it("supports signals without payloads", () => {
+    let count = 0
+    const signal = new Signal()
+    signal.add(() => count++)
+    signal.emit()
+    expect(count).toEqual(1)
+  })
 })