<!DOCTYPE html>
<meta charset=utf-8>
<title>Printing</title>
<link rel=help href="https://html.spec.whatwg.org/#printing">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
setup({explicit_timeout: true})
</script>

<p>Click on the button below.</p>
<p>If the browser offers to print the current page, dismiss the prompt to
return to this page. The following should then appear in the box marked as
"Output":</p>
<pre>
before calling print()
beforeprint
afterprint
after calling print()
</pre>
<p>If no user dialog appears, either the above or the following should be
printed in the box marked as "Output":</p>
<pre>
before calling print()
after calling print()
</pre>
<p>The test passes if the above criteria are satisfied and "PASS" appears in a
table below this paragraph. The test fails otherwise.</p>

<button onclick="testBtn(this)">Click here!</button>
<h3>Output</h3>
<pre id=output></pre>

<script>
"use strict";
// This test is actually synchronous, but we use async_test()'s nice
// infrastructure around t.step() to capture errors in event listeners. This is
// necessary since it seems like in Chrome, exceptions in beforeprint/afterprint
// event listeners are not propagated to error events. See
// https://crbug.com/977828.
const t = async_test();
const log = [];
function out(str) {
  log.push(str);
  output.appendChild(document.createTextNode(str + "\n"));
}
function testBtn(btn) {
  btn.remove();
  window.addEventListener("beforeprint", function (ev) {
    // t.step_func() does not preserve `this`, which we test below.
    t.step(() => {
      out("beforeprint");
      assert_equals(Object.getPrototypeOf(ev), Event.prototype);
      assert_equals(this, window);
      assert_equals(ev.target, window);
      assert_equals(ev.type, "beforeprint");
    });
  });
  window.addEventListener("afterprint", function (ev) {
    // t.step_func() does not preserve `this`, which we test below.
    t.step(() => {
      out("afterprint");
      assert_equals(Object.getPrototypeOf(ev), Event.prototype);
      assert_equals(this, window);
      assert_equals(ev.target, window);
      assert_equals(ev.type, "afterprint");
    });
  });
  out("before calling print()");
  print();
  out("after calling print()");
  t.step(() => {
    try {
      assert_array_equals(log, [
        "before calling print()",
        "beforeprint",
        "afterprint",
        "after calling print()",
      ]);
    } catch (err) {
      try {
        assert_array_equals(log, [
          "before calling print()",
          "after calling print()",
        ]);
      } catch (err) {
        assert_unreached("Output does not match either possibility");
      }
    }
  });
  t.done();
}
</script>
