如何在菜单下拉菜单中创建平滑过渡？

Question

I'm trying to figure out how to make a smooth transition in my menu transition. I already wrote a function for the times to appear and disappear onclick, but I'm not sure how to style the transition.

Here's what I have so far:

HTML:

<nav id="menu">
  <h2>Menu</h2>
    <ul>
      <li id="toggleTitle">Projects <i class="fa fa-angle-down" aria-hidden="true"></i></li>
      <li class="projects projectsClass"><a href="#">Project 1</a></li>
      <li class="projects projectsClass"><a href="#">Project 2</a></li>
      <li class="projects projectsClass"><a href="#">Project 3</a></li>
    </ul>
 </nav>

JS:

//toggleProjects
var toggleProjects = function(){

//function
var projectsList=document.getElementsByClassName('projects');
// if(projectsList[0].style.display=='none'){
if(!projectsList[0].classList.contains('projectsClass')){
//reappear
for(var i=0; i<projectsList.length; i++){
  // projectsList[i].style.display='';
  projectsList[i].classList.add('projectsClass');
}

} else {
//disappear
for(var i=0; i<projectsList.length; i++){
  // projectsList[i].style.display='none';
  projectsList[i].classList.remove('projectsClass');
}
}
};

//event listener for click
document.getElementById('toggleTitle').addEventListener('click', 
toggleProjects);

CSS:

.projectsClass {
    display: none;
}

.projects {
    margin-left: 30px;
}

#menu > .toggleTitle {
    padding: 1em 0;
    line-height: 1.5;
    border: 0;
    color: white;
}

jsfiddlelink: https://jsfiddle.net/j2fygbzb/

Answer 1

I got it to do something similar to what you're expecting (or so i think) using your code and only some very slight css modifications. I added a transition css property to .projects here's a fiddle:

https://jsfiddle.net/j2fygbzb/9/

Here's the CSS i changed:

.projectsClass {
    max-height: 0 !important;
    visibility: hidden !important;
}

.projects {
    margin-left: 30px;
    max-height: 20px;
    visibility: visible;
    transition: all 0.5s;
}