doc-scroll-run-to-completion.html

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 <!-- This Source Code Form is subject to the terms of the Mozilla Public

    - License, v. 2.0. If a copy of the MPL was not distributed with this

    - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->

<!DOCTYPE html>

<meta charset=UTF-8>

<body></body>

<script>

const cpmm = SpecialPowers.Services.cpmm;

var result;

for (var i = 0; i < 100; i++) {

var div = document.createElement("div");

div.innerHTML = "Hello World!";

document.body.insertBefore(div, document.body.firstChild);

async function pauseOnce() {

    window.addEventListener('scroll', done);

    result = "test failed";

    debugger;

    result = "test passed";

function done() {

    cpmm.sendAsyncMessage(result);

</script>