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<!DOCTYPE html>
<div style="height: 300px"></div>
<script>
var is_setup = false;
var port;
var frame_id;
function postReplyMessage(command) {
const message_target = (port ? port : parent);
message_target.postMessage({
command: command,
frame_id: frame_id,
scrollTop: document.documentElement.scrollTop
}, "*");
}
function handleMessage(event) {
switch (event.data.command) {
case 'setup':
is_setup = false;
port = event.source;
frame_id = event.data.frame_id;
if (document.scrollingElement.scrollLeft != 0 ||
document.scrollingElement.scrollTop != 0) {
document.scrollingElement.scrollTo(0, 0);
} else {
is_setup = true;
postReplyMessage('setup');
}
break;
default:
break;
}
}
function handleScrollend() {
var command = 'onscrollend';
if (!is_setup &&
document.scrollingElement.scrollTop == 0 &&
document.scrollingElement.scrollLeft == 0) {
is_setup = true;
command = 'setup';
}
postReplyMessage(command);
}
window.addEventListener('message', handleMessage);
window.addEventListener('scrollend', handleScrollend);
</script>