added test for wasm log output

callback case for log test

tests/wasm/testdata/log.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"syscall/js"
+)
+
+func main() {
+
+	// try various log and other output directly
+	log.Println("log 1")
+	log.Print("log 2")
+	log.Printf("log %d\n", 3)
+	println("println 4")
+	fmt.Println("fmt.Println 5")
+	log.Printf("log %s", "6")
+
+	// now set up some log output in a button click callback
+	js.Global().
+		Get("document").
+		Call("querySelector", "#main").
+		Set("innerHTML", `<button id="testbtn">Test</button>`)
+
+	js.Global().
+		Get("document").
+		Call("querySelector", "#testbtn").
+		Call("addEventListener", "click",
+			js.FuncOf(func(this js.Value, args []js.Value) interface{} {
+				println("in func 1")
+				log.Printf("in func 2")
+				return nil
+			}))
+
+	// click the button
+	js.Global().
+		Get("document").
+		Call("querySelector", "#testbtn").
+		Call("click")
+
+}