How to add onclick to a html element dynamically using javascript

add an eventlistener to the element which has a defined function to call :

elem.addEventListener("click", func, false); //where func is your function name

https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener

The best way which i found out for myself is like below.

const li = document.createElement('li');
        li.innerText = "client";
        li.id ="key";
        li.className = "client-class";
        li.setAttribute("onclick","valid;");