How can I make a dropdown close automatically if an other one is clicked?

In the HTML included, there are 3 dropdown buttons with 3 "links" each. How can I close all other dropdowns when one of them is clicked?

This is my code:

for (i = 0; i < dropdown.length; i++) {
  dropdown[i].addEventListener("click", function() {
  this.classList.toggle("active");
  var dropdownContent = this.nextElementSibling;
  if (dropdownContent.style.display === "block") {
  dropdownContent.style.display = "none";
  } else {
  dropdownContent.style.display = "block";
  }
  });
}

body {
  font-family: "Lato", sans-serif;
}
 
/* Fixed sidenav, full height */
.sidenav {
  height: 100%;
  width: 200px;
  position: fixed;
  z-index: 1;
  top: 0;
  left: 0;
  background-color: #111;
  overflow-x: hidden;
  padding-top: 20px;
}
 
/* Style the sidenav links and the dropdown button */
.sidenav a, .dropdown-btn {
  padding: 6px 8px 6px 16px;
  text-decoration: none;
  font-size: 20px;
  color: #818181;
  display: block;
  border: none;
  background: none;
  width: 100%;
  text-align: left;
  cursor: pointer;
  outline: none;
}
 
/* On mouse-over */
.sidenav a:hover, .dropdown-btn:hover {
  color: #f1f1f1;
}
 
/* Add an active class to the active dropdown button */
.active {
  background-color: blue;
  color: white;
}
 
/* Dropdown container (hidden by default). Optional: add a lighter background color and some left padding to change the design of the dropdown content */
.dropdown-container {
  display: none;
  background-color: #262626;
  padding-left: 8px;
}
 
/* Optional: Style the caret down icon */
.fa-caret-down {
  float: right;
  padding-right: 8px;
}
 
/* Some media queries for responsiveness */
@media screen and (max-height: 450px) {
  .sidenav {padding-top: 15px;}
  .sidenav a {font-size: 18px;}
}

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
 
<div class="sidenav">
    <button class="dropdown-btn">Dropdown1 
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-container">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
  <button class="dropdown-btn">Dropdown2 
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-container">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
    <button class="dropdown-btn">Dropdown3 
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-container">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
</div>
 
<script>
/* Loop through all dropdown buttons to toggle between hiding and showing its dropdown content - This allows the user to have multiple dropdowns without any conflict */
var dropdown = document.getElementsByClassName("dropdown-btn");
var i;
 
for (i = 0; i < dropdown.length; i++) {
  dropdown[i].addEventListener("click", function() {
  this.classList.toggle("active");
  var dropdownContent = this.nextElementSibling;
  if (dropdownContent.style.display === "block") {
  dropdownContent.style.display = "none";
  } else {
  dropdownContent.style.display = "block";
  }
  });
}
</script>
 
</body>
</html>

Solution

try this modified javascript

var dropdown = document.getElementsByClassName("dropdown-btn");
var i;
var next;
for (i = 0; i < dropdown .length; i++) {
    dropdown [i].onclick = function() {
        if(next){
            next.classList.toggle("active",false);
            next.nextElementSibling.style.display = "none";
        }
        this.classList.toggle("active");
        this.nextElementSibling.style.display = "block";
        next=this;
    }
}

var dropdown = document.getElementsByClassName("dropdown-btn");
var i;
var next;
for (i = 0; i < dropdown .length; i++) {
    dropdown [i].onclick = function() {
        if(next){
            next.classList.toggle("active",false);
            next.nextElementSibling.style.display = "none";
        }
        this.classList.toggle("active");
        this.nextElementSibling.style.display = "block";
        next=this;
    }
}

body {
  font-family: "Lato", sans-serif;
}

/* Fixed sidenav, full height */
.sidenav {
  height: 100%;
  width: 200px;
  position: fixed;
  z-index: 1;
  top: 0;
  left: 0;
  background-color: #111;
  overflow-x: hidden;
  padding-top: 20px;
}

/* Style the sidenav links and the dropdown button */
.sidenav a, .dropdown-btn {
  padding: 6px 8px 6px 16px;
  text-decoration: none;
  font-size: 20px;
  color: #818181;
  display: block;
  border: none;
  background: none;
  width: 100%;
  text-align: left;
  cursor: pointer;
  outline: none;
}

/* On mouse-over */
.sidenav a:hover, .dropdown-btn:hover {
  color: #f1f1f1;
}

/* Add an active class to the active dropdown button */
.active {
  background-color: blue;
  color: white;
}

/* Dropdown container (hidden by default). Optional: add a lighter background color and some left padding to change the design of the dropdown content */
.dropdown-container {
  display: none;
  background-color: #262626;
  padding-left: 8px;
}

/* Optional: Style the caret down icon */
.fa-caret-down {
  float: right;
  padding-right: 8px;
}

/* Some media queries for responsiveness */
@media screen and (max-height: 450px) {
  .sidenav {padding-top: 15px;}
  .sidenav a {font-size: 18px;}
}

<html>
<body>

<div class="sidenav">
    <button class="dropdown-btn">Dropdown1 
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-container">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
  <button class="dropdown-btn">Dropdown2 
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-container">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
    <button class="dropdown-btn">Dropdown3 
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-container">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
</div>


</body>
</html>