替换所选文本并将HTML保留在所选文本

Question

是否可以替换所选文本并保留HTML（跨选定文本）？

我想在按钮单击时将文本设置为Upper或Lower，并将html标记范围保留在所选文本中。我的代码看起来像这样。

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function replaceSelectedText(replacementText) {
    var sel, range;
    var selectedText=window.getSelection().toString();
  // Pokud je oznaceny text a je obsazen v divu 'zprava'
    if ($.trim(selectedText)!="") {
        if (window.getSelection) {
            sel = window.getSelection();
            if (sel.rangeCount) {
                range = sel.getRangeAt(0);
                range.deleteContents();
                range.insertNode(document.createTextNode(replacementText));
            }
        } else if (document.selection && document.selection.createRange) {
            range = document.selection.createRange();
            range.text = replacementText;
        }
    }
}

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<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<p contenteditable>DJSH SAJKDH ASDK ahsjkda sdasd <span style="color:red">asjda lsdjkl LASJD ASLdkja sdlASdjk aůskjd aůSdkj asdů</span></p>
<button type="button" class="btn btn-default" onclick="replaceSelectedText(window.getSelection().toString().toLowerCase());">a&#8595;</button>
<button type="button" class="btn btn-default" onclick="replaceSelectedText(window.getSelection().toString().toUpperCase());">A&#8593;</button>

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