third_party/web_platform_tests/dom/nodes/CharacterData-surrogates.html

<!DOCTYPE html>
<meta charset=utf-8>
<title>Splitting and joining surrogate pairs in CharacterData methods</title>
<link rel=help href="https://dom.spec.whatwg.org/#dom-characterdata-substringdata">
<link rel=help href="https://dom.spec.whatwg.org/#dom-characterdata-replacedata">
<link rel=help href="https://dom.spec.whatwg.org/#dom-characterdata-insertdata">
<link rel=help href="https://dom.spec.whatwg.org/#dom-characterdata-deletedata">
<link rel=help href="https://dom.spec.whatwg.org/#dom-characterdata-data">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="log"></div>
<script>
function testNode(create, type) {
  test(function() {
    var node = create()
    assert_equals(node.data, "test")

    node.data = "🌠 test 🌠 TEST"

    assert_equals(node.substringData(1, 8), "\uDF20 test \uD83C")
  }, type + ".substringData() splitting surrogate pairs")

  test(function() {
    var node = create()
    assert_equals(node.data, "test")

    node.data = "🌠 test 🌠 TEST"

    node.replaceData(1, 4, "--");
    assert_equals(node.data, "\uD83C--st 🌠 TEST");

    node.replaceData(1, 2, "\uDF1F ");
    assert_equals(node.data, "🌟 st 🌠 TEST");

    node.replaceData(5, 2, "---");
    assert_equals(node.data, "🌟 st---\uDF20 TEST");

    node.replaceData(6, 2, " \uD83D");
    assert_equals(node.data, "🌟 st- 🜠 TEST");
  }, type + ".replaceData() splitting and creating surrogate pairs")

  test(function() {
    var node = create()
    assert_equals(node.data, "test")

    node.data = "🌠 test 🌠 TEST"

    node.deleteData(1, 4);
    assert_equals(node.data, "\uD83Cst 🌠 TEST");

    node.deleteData(1, 4);
    assert_equals(node.data, "🌠 TEST");
  }, type + ".deleteData() splitting and creating surrogate pairs")

  test(function() {
    var node = create()
    assert_equals(node.data, "test")

    node.data = "🌠 test 🌠 TEST"

    node.insertData(1, "--");
    assert_equals(node.data, "\uD83C--\uDF20 test 🌠 TEST");

    node.insertData(1, "\uDF1F ");
    assert_equals(node.data, "🌟 --\uDF20 test 🌠 TEST");

    node.insertData(5, " \uD83D");
    assert_equals(node.data, "🌟 -- 🜠 test 🌠 TEST");
  }, type + ".insertData() splitting and creating surrogate pairs")
}

testNode(function() { return document.createTextNode("test") }, "Text")
testNode(function() { return document.createComment("test") }, "Comment")
</script>