How to hide a dropdown when the user clicks outside of it

In this case, On onblur you could call a function which fires the undropdown(0); after a very tiny setTimeout almost instantly. Like so:

function set() {
  setTimeout(function(){ 
    undropdown(0);
  }, 100);
}

HTML

<input type="text" name="class" placeholder="Class" onfocus="dropdown(0)" onblur="set()" />

No other change is required.

function input(pos) {
  var dropdown = document.getElementsByClassName('drop');
  var li = dropdown[0].getElementsByTagName("li");

  document.getElementsByTagName('input')[0].value = li[pos].innerHTML;
  undropdown(0);
}

function dropdown(pos) {
  document.getElementsByClassName('content')[pos].style.display= "block"
}

function undropdown(pos) {
  document.getElementsByClassName('content')[pos].style.display= "none";
}

function set() {
  setTimeout(function(){ 
    undropdown(0);
  }, 100);
}
        .drop {
            position: relative;
            display: inline-block;
            vertical-align:top;
            overflow: visible;
        }

        .content {
            display: none;
            list-style-type: none;
            border: 1px solid #000; 
            padding: 0;
            margin: 0;
            position: absolute;
            z-index: 2;
            width: 100%;
            max-height: 190px;
            overflow-y: scroll;
        }

        .content li {
            padding: 12px 16px;
            display: block;
            margin: 0;
        }
   <div class="drop">
        <input type="text" name="class" placeholder="Class" onfocus="dropdown(0)" onblur="set()" />
        <ul class="content">
            <li onclick="input(0)">Option 1</li>
            <li onclick="input(1)">Option 2</li>
            <li onclick="input(2)">Option 3</li>
            <li onclick="input(3)">Option 4</li>
        </ul>
    </div>


You could make the dropdown focusable with tabindex, and in the input's blur event listener only hide the dropdown if the focus didn't go to the dropdown (see When onblur occurs, how can I find out which element focus went to?)

<ul class="content" tabindex="-1"></ul>

input.addEventListener('blur', function(e) {
  if(!e.relatedTarget || !e.relatedTarget.classList.contains('content')) {
    undropdown(0);
  }
});


function input(e) {
  var dropdown = document.getElementsByClassName('drop');
  var li = dropdown[0].getElementsByTagName("li");
  document.getElementsByTagName('input')[0].value = e.target.textContent;
  undropdown(0);
}
[].forEach.call(document.getElementsByTagName('li'), function(el) {
  el.addEventListener('click', input);
});
function dropdown(pos) {
  document.getElementsByClassName('content')[pos].style.display = "block"
}
function undropdown(pos) {
  document.getElementsByClassName('content')[pos].style.display = "none";
}
var input = document.getElementsByTagName('input')[0];
input.addEventListener('focus', function(e) {
  dropdown(0);
});
input.addEventListener('blur', function(e) {
  if(!e.relatedTarget || !e.relatedTarget.classList.contains('content')) {
    undropdown(0);
  }
});
.drop {
  position: relative;
  display: inline-block;
  vertical-align: top;
  overflow: visible;
}
.content {
  display: none;
  list-style-type: none;
  border: 1px solid #000;
  padding: 0;
  margin: 0;
  position: absolute;
  z-index: 2;
  width: 100%;
  max-height: 190px;
  overflow-y: scroll;
  outline: none;
}
.content li {
  padding: 12px 16px;
  display: block;
  margin: 0;
}
<div class="drop">
  <input type="text" name="class" placeholder="Class" />
  <ul class="content" tabindex="-1">
    <li>Option 1</li>
    <li>Option 2</li>
    <li>Option 3</li>
    <li>Option 4</li>
  </ul>
</div>

Tags:

Javascript

Html

Css

Drop Down Menu

Input

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