mess around with support WASM builds

app/demo/log.go

@@ -0,0 +1,42 @@
+package main
+
+import "syscall/js"
+
+type LogWriter struct {
+	Element   js.Value
+	Container js.Value
+}
+
+func (pw *LogWriter) ScrollToBottom() {
+	scrollHeight := pw.Container.Get("scrollHeight").Int()
+	clientHeight := pw.Container.Get("clientHeight").Int()
+	pw.Container.Set("scrollTop", scrollHeight-clientHeight)
+}
+
+func (pw *LogWriter) IsScrolledToBottom() bool {
+	scrollHeight := pw.Container.Get("scrollHeight").Int()
+	clientHeight := pw.Container.Get("clientHeight").Int()
+	scrollTop := pw.Container.Get("scrollTop").Int()
+	return scrollHeight-clientHeight <= scrollTop+25
+}
+
+func (pw *LogWriter) Write(p []byte) (n int, err error) {
+	if !pw.Element.IsUndefined() {
+		currentText := pw.Element.Get("textContent").String()
+		newText := currentText + string(p)
+		pw.Element.Set("textContent", newText)
+		if pw.IsScrolledToBottom() {
+			pw.ScrollToBottom()
+		}
+	}
+	return len(p), nil
+}
+
+func NewLogWriter(id string) *LogWriter {
+	element := document.Call("getElementById", id)
+	container := element.Get("parentElement")
+	return &LogWriter{
+		Element:   element,
+		Container: container,
+	}
+}