Calling a GDscript function in JavaScript

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1

Godot Version

3.6

Question

I am creating a Godot game that is embedded in an HTML page. I want to be able to call a Godot function from JavaScript (on the click of a button). I am having trouble getting my code to work.

Here is my GDscript code (RobotController.gd):

extends Spatial

var robot
func _ready() -> void:
	print("init")
	robot = get_node("../Robot")
	var callback = JavaScript.create_callback(self, "receivedMessage")
	if OS.has_feature("JavaScript"):
		print("has js")
		var window = JavaScript.get_interface("window")
		window.onmessage = callback
	else:
		print("no js")
	
func receivedMessage(args):
	print ("recieved message")
	robot.moveForward()
	# parse
	var key
	if args[0].message:
		key = 'message'
	else:
		key = 'data'
	var data = args[0][key]
	
	# filter
	if data.find('toGodot:') == 0:
		# message starts with 'toGodot:'
		data = data.replace('toGodot:', '')
		if (data == "moveForward"):
			robot.moveForward()

My HTML file containing my JavaScript code (index.html) is:

<!DOCTYPE html>
<html>
<head>
    <title>Test Godot</title>
    <meta charset="UTF-8">
</head>
<body>
    <iframe id="canvas" src="godot.html" style="width: 50%; height: 300px; border: 1px solid black;"></iframe>
    <button id="moveForwardButton" onclick="moveForward()">Move Forward</button>

    <script src="godot.js"></script>
    <script>

        var iframe = document.getElementById("canvas");
        var gdBase = "toGodot:";
        
        function moveForward(){
            //console.log("clicked");
            iframe.contentWindow.postMessage(gdBase + 'moveForward', '*');
        }
    </script>
</body>
</html>

I am having a lot of trouble getting Godot to receive the message. I based my code off of a solution here, but am unable to get it to work. Any help/advice is appreciated. Thanks in advance!