Close sidebar menu when click outside of it and when click on menu item

The target is to close the sidebar menu when I click outside of it or when I click on one of the menu item. I've created the two working functions in Javascript to open and close the menu, clicking on the toggle:

function openNav() {
  document.getElementById("#sideMenu").style.width = "250px";
}

function closeNav() {
  document.getElementById("#sideMenu").style.width = "0";
}

function clickOutsite() {
  TO - DO
}

function clickOnItemAndClose() {
  TO - DO
}

<div class="header"></div>
<input type="checkbox" class="openSideMenu" id="openSideMenu">
<label for="openSideMenu" class="sideIconToggle" onclick="openNav()">
            <div class="spinner diagonal part-1"></div>
            <div class="spinner horizontal"></div>
            <div class="spinner diagonal part-2"></div>
            </label>
<div id="sideMenu">
  <ul class="sideMenuInner">
    <li class="active"><a href="#" data-toggle="tab">Item1</a></li>
    <li><a href="#" data-toggle="tab">Item2</a></li>
    <li><a href="#" data-toggle="tab">Item3</a></li>
  </ul>
</div>

I've tried to create an overlay layer and create a function connected to it, but the result is not valid.

Could you help me, please? Thanks in advance

Edit: here there is a demo https://codepen.io/Clara83/pen/PoPVMgN

Solution

The whole animation of hide/show is based off CSS so you just need to toggle the checked property of the checkbox <input type="checkbox" class="openSideMenu" id="openSideMenu">

To solve the problem of detecting click outside you can wrap the sidebar in a div and then use contains property of event object that gets emitted from the element being clicked

function hideSidebar() {
  document.getElementById('openSideMenu').checked = false;
}

var sideIconToggle = document.getElementById('sidebarContainer');

document.addEventListener('click', function(event) {
  if (!sidebarContainer.contains(event.target))
    hideSidebar();
});

html,
body {
  overflow-x: hidden;
  height: 100%;
}

body {
  background: #fff;
  padding: 0;
  margin: 0;
  font-family: 'Varela Round', sans-serif;
}

.header {
  display: block;
  margin: 0 auto;
  width: 100%;
  max-width: 100%;
  box-shadow: none;
  background-color: black;
  position: fixed;
  height: 60px!important;
  overflow: hidden;
  z-index: 10;
}

.main {
  margin: 0 auto;
  display: block;
  height: 100%;
  margin-top: 60px;
}

.mainInner {
  display: table;
  height: 100%;
  width: 100%;
  text-align: center;
}

.mainInner div {
  display: table-cell;
  vertical-align: middle;
  font-size: 3em;
  font-weight: bold;
  letter-spacing: 1.25px;
}

#sideMenu {
  height: 100%;
  position: fixed;
  left: 0;
  width: 250px;
  margin-top: 60px;
  transform: translateX(-250px);
  transition: transform 250ms ease-in-out;
  background: grey;
  z-index: 1;
}

.sideMenuInner {
  margin: 0;
  padding: 0;
  border-top: 1px solid black;
}

.sideMenuInner li {
  list-style: none;
  color: #fff;
  text-transform: uppercase;
  font-weight: bold;
  padding: 20px;
  cursor: pointer;
  border-bottom: 1px solid black;
}

.sideMenuInner li span {
  display: block;
  font-size: 14px;
  color: rgba(255, 255, 255, 0.50);
}

.sideMenuInner li a {
  color: #fff;
  text-transform: uppercase;
  font-weight: bold;
  cursor: pointer;
  text-decoration: none;
}

input[type="checkbox"]:checked~#sideMenu {
  transform: translateX(0);
}

input[type=checkbox] {
  transition: all 0.3s;
  box-sizing: border-box;
  display: none;
}

.sideIconToggle {
  transition: all 0.3s;
  box-sizing: border-box;
  cursor: pointer;
  position: absolute;
  z-index: 99;
  height: 100%;
  width: 100%;
  top: 22px;
  left: 15px;
  height: 22px;
  width: 22px;
}

.spinner {
  transition: all 0.3s;
  box-sizing: border-box;
  position: absolute;
  height: 3px;
  width: 100%;
  background-color: #fff;
}

.horizontal {
  transition: all 0.3s;
  box-sizing: border-box;
  position: relative;
  float: left;
  margin-top: 3px;
}

.diagonal.part-1 {
  position: relative;
  transition: all 0.3s;
  box-sizing: border-box;
  float: left;
}

.diagonal.part-2 {
  transition: all 0.3s;
  box-sizing: border-box;
  position: relative;
  float: left;
  margin-top: 3px;
}

input[type=checkbox]:checked~.sideIconToggle>.horizontal {
  transition: all 0.3s;
  box-sizing: border-box;
  opacity: 0;
}

input[type=checkbox]:checked~.sideIconToggle>.diagonal.part-1 {
  transition: all 0.3s;
  box-sizing: border-box;
  transform: rotate(135deg);
  margin-top: 8px;
}

input[type=checkbox]:checked~.sideIconToggle>.diagonal.part-2 {
  transition: all 0.3s;
  box-sizing: border-box;
  transform: rotate(-135deg);
  margin-top: -9px;
}

#sidenav-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 0;
  height: 100%;
  background: rgba(0, 0, 0, .1);
  cursor: pointer;
  z-index: 1;
}

<div class="header"></div>

<div id="sidebarContainer">
  <input type="checkbox" class="openSideMenu" id="openSideMenu">

  <label for="openSideMenu" class="sideIconToggle">
    <div class="spinner diagonal part-1"></div>
    <div class="spinner horizontal"></div>
    <div class="spinner diagonal part-2"></div>
  </label>

  <div id="sideMenu">
    <ul class="sideMenuInner">
      <li class="active" onclick="hideSidebar()"><a href="#" data-toggle="tab">Item1</a></li>
      <li onclick="hideSidebar()"><a href="#" data-toggle="tab">Item2</a></li>
      <li onclick="hideSidebar()"><a href="#" data-toggle="tab">Item3</a></li>
    </ul>
  </div>
</div>