Only show active dropdown menu content - multiple dropdown buttons in a navbar

I have a navbar that has multiple buttons that on click display a dropdown menu. What happens is when I click a button it shows dropdown menu, then when I click outside the menu it hides the active menu which is right.

See screenshot here...

       function myFunction(num) {
          document.getElementById("myDropdown" + num).classList.toggle("show"); 
       }
       
       window.onclick = function(event) {
          if (!event.target.matches('.dropbtn')) {
             var dropdowns = document.getElementsByClassName("dropdown-content");
             var i;
             for (i = 0; i < dropdowns.length; i++) {
                var openDropdown = dropdowns[i];
                if (openDropdown.classList.contains('show')) {
                   openDropdown.classList.remove('show');
                }
             }
          }
       }

.ul {
  
}
header {
    position: fixed;
    right: 0;
    top: 0;
    left: 0;
    z-index: 100;
    height: 60px;
    box-shadow: 0px 5px 5px -5px rgb(0 0 0 /10%);
    background: #4891c4;;
    color: #ffffff;
    transition: left 300ms;
}

.header-content {
    position: relative;
    top: 0;
    width: 200px;
    height: 60px;
    float: right;
    align-items: center;
    justify-content: center;
}

.header-content, .header-menu {
    display: flex;
    align-items: center;
}

.header-content {
    justify-content: space-between;
    padding: 0rem 1rem;
}

.header-content label:first-child span {
    font-size: 1.3rem;
}

.header-content label {
    cursor: pointer;
}

.arrow_box {
    top: 10px;
    position: relative;
    border: 1px solid #aaa;         /*set border colour here*/
    width: 300px;
    height: auto;
    background-color: #d6eef9;      /*set menu container background color here*/
    border-radius: 3px;
    -webkit-filter: drop-shadow(0 1px 10px rgba(113, 158, 206, 0.8)); /*set shadow colour  and size here*/
    -moz-box-shadow: 0 1px 10px rgba(113, 158, 206, 0.8);
    filter: drop-shadow(0 1px 10px rgba(113, 158, 206, 0.8));
}

.arrow_box:after,
.arrow_box:before {
    bottom: 100%;
    border: solid transparent;
    content: " ";
    height: 0;
    width: 0;
    position: absolute;
    pointer-events: none;
}

.arrow_box:after {
    border-color: rgba(255, 255, 255, 0);
    border-bottom-color: #d6eef9;
    border-width: 10px;
    right: 8px;
    margin-right: 0px;
}

.dropdown { 
    display: flex;
    height: 40px;
    width: 40px;
    border-radius: 50%;
    position: relative;
    justify-content: center;
    align-items: center;    
    margin-right: 1rem;
}

.dropdown-content {
    display: none;
    position: absolute;
    min-width: 160px;
    overflow: none;
    z-index: 1;
    right: 0;
    margin-right: 0rem;
    top: calc(100% + 0rem);
}
  
.header-dropdown {
    background-color: #d6eef9; 
}

.header-dropdown ul li:hover {
    background: #d8e2ec;
}
.header-dropdown ul {
    list-style-type: none;
    padding: 0;
    text-align: center;
}
.header-dropdown a {
    text-decoration: none;
    color: var(--menu-color);
    display: block;
    padding: 0.5rem 0rem 0.5rem 1rem;   /* control menu height here */
    text-align: left;       /* control menu text align here center, left or right */
}
.header-dropdown a span {
    min-height: 15px;
    display: inline-flex;
    align-items: center;
    font-size: 1.7rem;
    margin: 0rem 0.5rem 0rem 0.5rem !important;
}
.header-dropdown a span, .header-dropdown a small {
    color: #327091;
}
.header-dropdown a small {
    font-size: 0.95rem;                             /* Sidebar font size */
    font-weight: normal;
    margin: 0rem 1rem 0rem 1rem !important;
    font-family: 'Open Sans', sans-serif;
}

 
.dropbtn {
    border: none;
    cursor: pointer;
}

.show {
    display: block;
}

.notification { 
    display: flex;
    height: 30px;
    width: 30px;
    border-radius: 50%;
    position: relative;
    cursor: pointer;
    color: white;
    padding: 1px;       
    font-size: 1.8rem;
    justify-content: center;
    align-items: center;
}

.badge {
    display: flex;
    position: absolute;
    background: red;
    height: 7px;
    width: 7px;
    justify-content: center;
    align-items: center;
    border-radius: 50%;
    right: -7px;
    top: -7px;
    padding: 8px;
    color: #fff;
    font-size: .8rem;
    font-weight: 500;
}

<link rel="stylesheet" href="https://maxst.icons8.com/vue-static/landings/line-awesome/line-awesome/1.3.0/css/line-awesome.min.css">

<header>
<div class="header-content">
    <div class="dropdown">
        <a>
          <div onclick="myFunction(1)" href="#" class="notification dropbtn las la-envelope"></div>
          <span onclick="myFunction(1)" class="badge dropbtn">4</span>
        </a>
        
        <div id="myDropdown1" class="dropdown-content">                 
                <div class="arrow_box">
                    <div class="header-dropdown">
                         <ul>
                            <li><a href=""><small>Message content</small></a></li>
                            <li><a href=""><small>Message content</small></a></li>
                        </ul>                   
                    </div>
                </div>
            </div>
    </div>
    
    <div class="dropdown">
        <a>
          <div onclick="myFunction(2)" href="#" class="notification dropbtn las la-bell"></div>
          <span onclick="myFunction(2)" class="badge dropbtn">8</span>
        </a>
        
        <div id="myDropdown2" class="dropdown-content">                 
            <div class="arrow_box">
                <div class="header-dropdown">
                     <ul>
                        <li><a href=""><span class="las la-question"><small>FAQ</small></span></a></li>
                        <li><a href=""><span class="las la-user"><small>Profile</small></span></a></li>
                        <li><a href=""><span class="las la-cog"><small>Settings</small></span></a></li>
                        <li><a href=""><span class="las la-sign-out-alt"><small>Log out</small></span></a></li>
                    </ul>                   
                </div>
            </div>
        </div>
    </div>
</div>
</header>

The problem is: when I click a button it shows dropdown menu, then when I click another button last menu is still showing and not disappearing, that means it will show two menu contents at the same time.

I need to hide last menu content and show active last menu content.

Solution

When opening a menu, you need to remove the class show from other menu items.

I modified your myFunction to the below code. If the clicked element already have the show class, it will be removed. Else the forEach will loop through all menu items and remove the show class from them.

function myFunction(num) {
  if (document.getElementById("myDropdown" + num).classList.contains('show')) {
    document.getElementById("myDropdown" + num).classList.remove('show');
    return;
  }
  Array.from(document.getElementsByClassName("dropdown-content")).forEach(x => {
    if (x.classList.contains('show'))
      x.classList.remove('show');
  });
  document.getElementById("myDropdown" + num).classList.toggle("show");
}

Working example.

function myFunction(num) {
  if (document.getElementById("myDropdown" + num).classList.contains('show')) {
    document.getElementById("myDropdown" + num).classList.remove('show');
    return;
  }
  Array.from(document.getElementsByClassName("dropdown-content")).forEach(x => {
    if (x.classList.contains('show'))
      x.classList.remove('show');
  });
  document.getElementById("myDropdown" + num).classList.toggle("show");
}

window.onclick = function(event) {
  if (!event.target.matches('.dropbtn')) {
    var dropdowns = document.getElementsByClassName("dropdown-content");
    var i;
    for (i = 0; i < dropdowns.length; i++) {
      var openDropdown = dropdowns[i];
      if (openDropdown.classList.contains('show')) {
        openDropdown.classList.remove('show');
      }
    }
  }
}

.ul {}

header {
  position: fixed;
  right: 0;
  top: 0;
  left: 0;
  z-index: 100;
  height: 60px;
  box-shadow: 0px 5px 5px -5px rgb(0 0 0 /10%);
  background: #4891c4;
  ;
  color: #ffffff;
  transition: left 300ms;
}

.header-content {
  position: relative;
  top: 0;
  width: 200px;
  height: 60px;
  float: right;
  align-items: center;
  justify-content: center;
}

.header-content,
.header-menu {
  display: flex;
  align-items: center;
}

.header-content {
  justify-content: space-between;
  padding: 0rem 1rem;
}

.header-content label:first-child span {
  font-size: 1.3rem;
}

.header-content label {
  cursor: pointer;
}

.arrow_box {
  top: 10px;
  position: relative;
  border: 1px solid #aaa;
  /*set border colour here*/
  width: 300px;
  height: auto;
  background-color: #d6eef9;
  /*set menu container background color here*/
  border-radius: 3px;
  -webkit-filter: drop-shadow(0 1px 10px rgba(113, 158, 206, 0.8));
  /*set shadow colour  and size here*/
  -moz-box-shadow: 0 1px 10px rgba(113, 158, 206, 0.8);
  filter: drop-shadow(0 1px 10px rgba(113, 158, 206, 0.8));
}

.arrow_box:after,
.arrow_box:before {
  bottom: 100%;
  border: solid transparent;
  content: " ";
  height: 0;
  width: 0;
  position: absolute;
  pointer-events: none;
}

.arrow_box:after {
  border-color: rgba(255, 255, 255, 0);
  border-bottom-color: #d6eef9;
  border-width: 10px;
  right: 8px;
  margin-right: 0px;
}

.dropdown {
  display: flex;
  height: 40px;
  width: 40px;
  border-radius: 50%;
  position: relative;
  justify-content: center;
  align-items: center;
  margin-right: 1rem;
}

.dropdown-content {
  display: none;
  position: absolute;
  min-width: 160px;
  overflow: none;
  z-index: 1;
  right: 0;
  margin-right: 0rem;
  top: calc(100% + 0rem);
}

.header-dropdown {
  background-color: #d6eef9;
}

.header-dropdown ul li:hover {
  background: #d8e2ec;
}

.header-dropdown ul {
  list-style-type: none;
  padding: 0;
  text-align: center;
}

.header-dropdown a {
  text-decoration: none;
  color: var(--menu-color);
  display: block;
  padding: 0.5rem 0rem 0.5rem 1rem;
  /* control menu height here */
  text-align: left;
  /* control menu text align here center, left or right */
}

.header-dropdown a span {
  min-height: 15px;
  display: inline-flex;
  align-items: center;
  font-size: 1.7rem;
  margin: 0rem 0.5rem 0rem 0.5rem !important;
}

.header-dropdown a span,
.header-dropdown a small {
  color: #327091;
}

.header-dropdown a small {
  font-size: 0.95rem;
  /* Sidebar font size */
  font-weight: normal;
  margin: 0rem 1rem 0rem 1rem !important;
  font-family: 'Open Sans', sans-serif;
}

.dropbtn {
  border: none;
  cursor: pointer;
}

.show {
  display: block;
}

.notification {
  display: flex;
  height: 30px;
  width: 30px;
  border-radius: 50%;
  position: relative;
  cursor: pointer;
  color: white;
  padding: 1px;
  font-size: 1.8rem;
  justify-content: center;
  align-items: center;
}

.badge {
  display: flex;
  position: absolute;
  background: red;
  height: 7px;
  width: 7px;
  justify-content: center;
  align-items: center;
  border-radius: 50%;
  right: -7px;
  top: -7px;
  padding: 8px;
  color: #fff;
  font-size: .8rem;
  font-weight: 500;
}

<!DOCTYPE html>
<html>

<head>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxst.icons8.com/vue-static/landings/line-awesome/line-awesome/1.3.0/css/line-awesome.min.css">
</head>

<body>

  <header>
    <div class="header-content">
      <div class="dropdown">
        <a>
          <div onclick="myFunction(1)" href="#" class="notification dropbtn las la-envelope"></div>
          <span onclick="myFunction(1)" class="badge dropbtn">4</span>
        </a>

        <div id="myDropdown1" class="dropdown-content">
          <div class="arrow_box">
            <div class="header-dropdown">
              <ul>
                <li><a href=""><small>Message content</small></a></li>
                <li><a href=""><small>Message content</small></a></li>
              </ul>
            </div>
          </div>
        </div>
      </div>

      <div class="dropdown">
        <a>
          <div onclick="myFunction(2)" href="#" class="notification dropbtn las la-bell"></div>
          <span onclick="myFunction(2)" class="badge dropbtn">8</span>
        </a>

        <div id="myDropdown2" class="dropdown-content">
          <div class="arrow_box">
            <div class="header-dropdown">
              <ul>
                <li><a href=""><span class="las la-question"><small>FAQ</small></span></a></li>
                <li><a href=""><span class="las la-user"><small>Profile</small></span></a></li>
                <li><a href=""><span class="las la-cog"><small>Settings</small></span></a></li>
                <li><a href=""><span class="las la-sign-out-alt"><small>Log out</small></span></a></li>
              </ul>
            </div>
          </div>
        </div>
      </div>

    </div>
  </header>
</body>

</html>