implement and use Content.getWebURL; mostly fixes #1279, although som…

…e issues with navigation remain

content/content.go

@@ -149,11 +149,15 @@ func (ct *Content) SetSource(source fs.FS) *Content {
 		}
 		return nil
 	}))
+	if url := ct.getWebURL(); url != "" {
+		ct.Open(url)
+		return ct
+	}
 	if root, ok := ct.pagesByURL[""]; ok {
 		ct.Open(root.URL)
-	} else {
-		ct.Open(ct.pages[0].URL)
+		return ct
 	}
+	ct.Open(ct.pages[0].URL)
 	return ct
 }
 

content/url_js.go

@@ -7,9 +7,11 @@
 package content
 
 import (
-	"fmt"
 	"net/url"
+	"strings"
 	"syscall/js"
+
+	"cogentcore.org/core/base/errors"
 )
 
 // firstContent is the first [Content] used for [Content.getWebURL] or [Content.saveWebURL],
@@ -18,6 +20,22 @@ var firstContent *Content
 
 var documentData = js.Global().Get("document").Get("documentElement").Get("dataset")
 
+// getWebURL returns the current relative web URL that should be passed to [Content.Open]
+// on startup and in [Content.handleWebPopState].
+func (ct *Content) getWebURL() string {
+	if firstContent == nil {
+		firstContent = ct
+	}
+	if firstContent != ct {
+		return ""
+	}
+	full, base, err := getURL()
+	if errors.Log(err) != nil {
+		return ""
+	}
+	return strings.TrimPrefix(full.String(), base.String())
+}
+
 // saveWebURL saves the current page URL to the user's address bar and history.
 func (ct *Content) saveWebURL() {
 	if firstContent == nil {
@@ -36,8 +54,7 @@ func (ct *Content) saveWebURL() {
 // handleWebPopState adds a JS event listener to handle user navigation in the browser.
 func (ct *Content) handleWebPopState() {
 	js.Global().Get("window").Call("addEventListener", "popstate", js.FuncOf(func(this js.Value, args []js.Value) any {
-		full, base, err := getURL()
-		fmt.Println(full, base, err)
+		ct.Open(ct.getWebURL())
 		return nil
 	}))
 }

content/url_noop.go

@@ -6,5 +6,6 @@
 
 package content
 
+func (ct *Content) getWebURL() string  { return "" }
 func (ct *Content) saveWebURL()        {}
 func (ct *Content) handleWebPopState() {}