Как добавить событие на клик в Toggle Menu?

function openNav() { 
    document.getElementById("mySidenav").style.width = "250px"; 
} 
 
function closeNav() { 
    document.getElementById("mySidenav").style.width = "0"; 
     
} 
 
function closeNav2() { 
    /*document.getElementById("about").style.width = "0";*/ 
    document.getElementById("mySidenav").style.width = "0"; 
}

function openNav() { 
  console.log("openNav"); 
  document.getElementById("mySidenav").style.width = "250px"; 
} 
 
function closeNav() { 
  console.log("closeNav"); 
  document.getElementById("mySidenav").style.width = "0"; 
} 
 
function closeNav2() { 
  console.log("closeNav2"); 
  document.getElementById("mySidenav").style.width = "0"; 
}

body { 
    font-family: "Lato", sans-serif; 
} 
 
.sidenav { 
    height: 100%; 
    width: 0; 
    position: fixed; 
    z-index: 1; 
    top: 0; 
    left: 0; 
    background-color: #111; 
    overflow-x: hidden; 
    transition: 0.5s; 
    padding-top: 60px; 
} 
 
.sidenav a { 
    padding: 1px 1px 1px 12px; 
    
    font-size: 21px; 
    color: #818181; 
    display: block; 
   
} 
 
.sidenav a:hover { 
    color: #f1f1f1; 
} 
 
.sidenav .closebtn { 
    position: absolute; 
    top: 0; 
    right: 25px; 
    font-size: 36px; 
    margin-left: 50px; 
} 
 
@media screen and (max-height: 450px) { 
  .sidenav {padding-top: 15px;} 
  .sidenav a {font-size: 18px;} 
}

<div id="mySidenav" class="sidenav"> 
  <a href="javascript:void(0)" class="closebtn" onclick="closeNav()">&times;</a> 
  <a href="#" id="about" onclick="closeNav2()">About</a> 
  <a href="#">Services</a> 
  <a href="#">Clients</a> 
  <a href="#">Contact</a> 
</div> 
 
<h2>Animated Sidenav Example</h2> 
<p>Click on the element below to open the side navigation menu.</p> 
<span style="font-size:30px;cursor:pointer" onclick="openNav()">&#9776; open</span>