refactor(api): move event's once to its own function (#1276)

.changes/js-event-once.md

@@ -0,0 +1,5 @@
+---
+"tauri-api": minor
+---
+
+The event listener `once` kind was moved to a dedicated function.

api/src/event.ts

@@ -4,5 +4,5 @@ async function emit(event: string, payload?: string): Promise<void> {
   return emitEvent(event, undefined, payload)
 }
 
-export { listen } from './helpers/event'
+export { listen, once } from './helpers/event'
 export { emit }

api/src/helpers/event.ts

@@ -7,16 +7,10 @@ export interface Event<T> {
 
 export type EventCallback<T> = (event: Event<T>) => void
 
-/**
- * listen to an event from the backend
- *
- * @param event the event name
- * @param handler the event handler callback
- */
-async function listen<T>(
+async function _listen<T>(
   event: string,
   handler: EventCallback<T>,
-  once = false
+  once: boolean
 ): Promise<void> {
   await invoke({
     __tauriModule: 'Event',
@@ -29,6 +23,32 @@ async function listen<T>(
   })
 }
 
+/**
+ * listen to an event from the backend
+ *
+ * @param event the event name
+ * @param handler the event handler callback
+ */
+async function listen<T>(
+  event: string,
+  handler: EventCallback<T>
+): Promise<void> {
+  return _listen(event, handler, false)
+}
+
+/**
+ * listen to an one-off event from the backend
+ *
+ * @param event the event name
+ * @param handler the event handler callback
+ */
+async function once<T>(
+  event: string,
+  handler: EventCallback<T>
+): Promise<void> {
+  return _listen(event, handler, true)
+}
+
 /**
  * emits an event to the backend
  *
@@ -51,4 +71,4 @@ async function emit(
   })
 }
 
-export { listen, emit }
+export { listen, once, emit }

api/src/window.ts

@@ -1,5 +1,5 @@
 import { invoke } from './tauri'
-import { EventCallback, emit, listen } from './helpers/event'
+import { EventCallback, emit, listen, once } from './helpers/event'
 
 interface WindowDef {
   label: string
@@ -33,14 +33,25 @@ class TauriWindow {
    *
    * @param event the event name
    * @param handler the event handler callback
-   * @param once unlisten after the first trigger if true
    */
   async listen<T>(
     event: string,
-    handler: EventCallback<T>,
-    once = false
+    handler: EventCallback<T>
   ): Promise<void> {
-    return listen(event, handler, once)
+    return listen(event, handler)
+  }
+
+  /**
+   * Listen to an one-off event emitted by the webview
+   *
+   * @param event the event name
+   * @param handler the event handler callback
+   */
+  async once<T>(
+    event: string,
+    handler: EventCallback<T>
+  ): Promise<void> {
+    return once(event, handler)
   }
 
   /**