introduce TaskOnce

ts/index.ts

@@ -1,7 +1,8 @@
-export {Task,ITaskFunction} from './taskbuffer.classes.task'
-export {Taskchain} from './taskbuffer.classes.taskchain'
-export {Taskparallel} from './taskbuffer.classes.taskparallel'
+export { Task, ITaskFunction } from './taskbuffer.classes.task'
+export { Taskchain } from './taskbuffer.classes.taskchain'
+export { Taskparallel } from './taskbuffer.classes.taskparallel'
 export { TaskManager } from './taskbuffer.classes.taskmanager'
+export { TaskOnce } from './taskbuffer.classes.taskonce'
 
 // import for naming only
 import './taskbuffer.classes.helpers'

ts/taskbuffer.classes.taskonce.ts

@@ -0,0 +1,24 @@
+import * as plugins from './taskbuffer.plugins'
+
+import { Task,  ITaskFunction} from './taskbuffer.classes.task'
+
+/**
+ * TaskOnce is run exactly once, no matter how often it is triggered
+ */
+export class TaskOnce extends Task {
+  hasTriggered: boolean = false
+  constructor (optionsArg: {
+    name?: string,
+    taskFunction: ITaskFunction
+  }) {
+    super({
+      name: optionsArg.name,
+      taskFunction: async () => {
+        if (!this.hasTriggered) {
+          this.hasTriggered = true
+          await optionsArg.taskFunction()
+        }
+      }
+    })
+  }
+}