无法在JavaScript中为已创建的DOM元素设置ID属性

你问题在于以下几点:

var dwarfButton = chatbox.appendChild(document.createElement("button")).textContent = "DWARF";
dwarfButton.setAttribute("id", "dwarf");

你在这里有一些链接,但最终你将dwarfButton变量设置为字符串"DWARF",而不是你创建的DOM元素.

试试这个:

var dwarfButton = document.createElement("button");
dwarfButton.textContent = "DWARF";
dwarfButton.setAttribute("id", "dwarf");
chatbox.appendChild(dwarfButton);