Search for siblings of elements in JavaScript

Given the element #elem:

<ul> <li>text</li> <li>text</li> <li id="elem">text</li> <li>text</li> <li>text</li> </ul>

Find its upper sibling element and add the text '!' to the end of it.

Given the element #elem:

<ul> <li>text</li> <li>text</li> <li id="elem">text</li> <li>text</li> <li>text</li> </ul>

Find its bottom sibling element and add the text '!' to the end of it.

Given the element #elem:

<ul> <li>text</li> <li>text</li> <li id="elem">text</li> <li>text</li> <li>text</li> </ul>

Find its bottom sibling of its bottom sibling (the next element after the next one) and add the text '!' to the end of it.

Given the element #elem:

<ul> <li>text1</li> <li>text2</li> <li id="elem">text3</li> <li>text4</li> <li>text5</li> </ul>

Swap the text of its upper sibling and the text of its bottom sibling.

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