The class is not added at the onclick event.

Incorrect use of classList It will be classList.add('class');

How can I find in the help

classList - This is a collection, not a function. Therefore, when you try to use it as a function, you get the corresponding exception: classList is not a function

There is also a help in the list of methods present in this collection.

To add, use the add method.

 var ul = document.querySelector("ul"); var li = ul.querySelectorAll("li"); var t; ul.onclick = function(e) { var target = e.target; if (target.tagName = "LI") { home(target); return; }; }; function home(node) { t = node; t.classList.add("oli") // не добавляется класс при нажатии } 

 .oli { background-color: red; } 

 <ul> <li>Первый</li> <li>Второй</li> <li>Третий</li> <li>Четвертый</li> <li>Пятый</li> </ul> 

classList is not a function, but a DOMTokenList object ( see also ).

 console.info(typeof document.querySelector('div').classList); // object 

 <div></div> 

Methods :
add() - Adds a value to the DOMTokenList object, if not present.

contains() - Checks whether the DOMTokenList object DOMTokenList passed value or not.

item() - Returns the value at the specified index.

remove() - Removes a value from the DOMTokenList object, if any.

toggle() - If the DOMTokenList contains the value passed to the method, it will be removed, otherwise it will be added.

They are more, but it is the most used

Properties :
length - The number of elements (or characters).