<!DOCTYPE html>
<html>
<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">
<head>
<style>
body, html {
    width: 100%;
    height: 100%;
    margin: 0;
}

#target {
    width: 100%;
    height: 100%;
    background: tomato;
}
</style>
</head>
<body>
<div id="target"></div>
<script>
function handleTouchEvent(event) {
    webkit.messageHandlers.testHandler.postMessage(event.type);
}

let target = document.getElementById("target");
target.addEventListener("touchstart", handleTouchEvent);
target.addEventListener("touchmove", handleTouchEvent);
target.addEventListener("touchcancel", handleTouchEvent);
target.addEventListener("touchend", handleTouchEvent);
</script>
</body>
</html>