Add support for JavaScript SpeechSynthesis API.

TTS.gd

@@ -1,27 +1,35 @@
 tool
 extends Node
 
-const TTS = preload("godot-tts.gdns")
+var TTS
 
 var tts = null
 
 func _ready():
-    # Only initialize TTS if it's available or if we're in the editor.
-    if TTS.can_instance() or Engine.editor_hint:
-        print_debug("Attempting to load TTS.")
-        tts = TTS.new()
+    if not OS.has_feature('JavaScript') and not Engine.has_singleton("AndroidTTS"):
+        TTS  = preload("godot-tts.gdns")
+    if OS.has_feature('JavaScript'):
+        pass
     elif Engine.has_singleton("AndroidTTS"):
         tts = Engine.get_singleton("AndroidTTS")
+    elif TTS.can_instance() or Engine.editor_hint:
+        tts = TTS.new()
     else:
         print_debug("TTS not available!")
 
+var javascript_rate = 50
+
 func set_rate(rate):
     if tts != null:
         tts.rate = rate
+    elif OS.has_feature('JavaScript'):
+        javascript_rate = rate
 
 func get_rate():
     if tts != null:
         return tts.rate
+    elif OS.has_feature('JavaScript'):
+        return javascript_rate
     else:
         return 0
 
@@ -31,14 +39,30 @@ func speak(text, interrupt := true):
     print_debug("%s: %s" % [text, interrupt])
     if tts != null:
         tts.speak(text, interrupt)
+    elif OS.has_feature('JavaScript'):
+        var scaled_rate = javascript_rate / 2
+        var code = """
+            let utterance = new SpeechSynthesisUtterance("%s")
+            utterance.rate = %s
+        """ % [text, scaled_rate]
+        if interrupt:
+            code += """
+                window.speechSynthesis.cancel()
+            """
+        code += "window.speechSynthesis.speak(utterance)"
+        JavaScript.eval(code)
 
 func stop():
     if tts != null:
         tts.stop()
+    elif OS.has_feature('JavaScript'):
+        JavaScript.eval("window.speechSynthesis.cancel()")
 
 func get_is_rate_supported():
     if Engine.get_singleton("AndroidTTS"):
         return false
+    elif OS.has_feature('JavaScript'):
+        return true
     elif tts != null:
         return tts.is_rate_supported()
     else: