test&doc: add example and update doc for function package

function/function.go

@@ -83,7 +83,7 @@ func Delay(delay time.Duration, fn any, args ...any) {
 	unsafeInvokeFunc(fn, args...)
 }
 
-// Debounced creates a debounced function that delays invoking fn until after wait duration have elapsed since the last time the debounced function was invoked..
+// Debounced creates a debounced function that delays invoking fn until after wait duration have elapsed since the last time the debounced function was invoked.
 // Play: https://go.dev/play/p/absuEGB_GN7
 func Debounced(fn func(), duration time.Duration) func() {
 	// Catch programming error while constructing the closure

function/watcher.go

@@ -3,12 +3,18 @@ package function
 import "time"
 
 // Watcher is used for record code excution time
+// Play: Todo
 type Watcher struct {
 	startTime int64
 	stopTime  int64
 	excuting  bool
 }
 
+// Start the watch timer.
+func NewWatcher() *Watcher {
+	return &Watcher{}
+}
+
 // Start the watch timer.
 func (w *Watcher) Start() {
 	w.startTime = time.Now().UnixNano()

function/watcher_example_test.go

@@ -0,0 +1,22 @@
+package function
+
+import "fmt"
+
+func ExampleWatcher() {
+	w := NewWatcher()
+
+	w.Start()
+
+	longRunningTask()
+
+	w.Stop()
+
+	// eapsedTime := w.GetElapsedTime().Milliseconds()
+
+	fmt.Println("foo")
+
+	w.Reset()
+
+	// Output:
+	// foo
+}

function/watcher_test.go

@@ -9,7 +9,7 @@ import (
 func TestWatcher(t *testing.T) {
 	assert := internal.NewAssert(t, "TestWatcher")
 
-	w := &Watcher{}
+	w := NewWatcher()
 	w.Start()
 
 	longRunningTask()