How to enable disabled inputs when multiple option is selected using javascript?

Question

I ran into a problem. How can I enable disabled inputs if I have selected multiple items in select tag and disable it again when I removed the selection?

<div class="form-group mb-3">
  <select class="selectpicker show-tick decore" name="state" id="state" multiple>
    <option value="one">one</option>
    <option value="two">two</option>
  </select>
</div>
<div class="input-group mb-3">
  <div class="input-group-prepend">
    <span class="input-group-text" id="basic-addon1">
      <i class="fas fa-child"></i>
    </span>
  </div>
  <input type="text" name="first" id="first" class="form-control" placeholder="first" aria-label="first" aria-describedby="basic-addon1" disabled />
</div>
<input type="text" name="second" id="second" class="form-control" placeholder="second" aria-label="second" aria-describedby="basic-addon1" disabled />
</div>

https://codepen.io/anon/pen/OrbQxm

Answer 1

Use change event handler for select tag and in function, check if length of selected option is less than 2 remove disabled attribute and if is great than 2 add it to element.

document.getElementById("state").onchange = function(){  
  var length = this.querySelectorAll("option:checked").length;
  document.querySelectorAll("#first, #second").forEach(function(ele){
    ele.disabled = length < 2;
  })
}

 document.getElementById("state").onchange = function(){ var length = this.querySelectorAll("option:checked").length; document.querySelectorAll("#first, #second").forEach(function(ele){ ele.disabled = length < 2; }) } 

 <div class="form-group mb-3"> <select class="selectpicker show-tick decore" name="state" id="state" multiple> <option value="one">one</option> <option value="two">two</option> </select> </div> <div class="input-group mb-3"> <div class="input-group-prepend"> <span class="input-group-text" id="basic-addon1"> <i class="fas fa-child"></i> </span> </div> <input type="text" name="first" id="first" class="form-control" placeholder="first" aria-label="first" aria-describedby="basic-addon1" disabled /> <input type="text" name="second" id="second" class="form-control" placeholder="second" aria-label="second" aria-describedby="basic-addon1" disabled /> </div> 

Also you can do this work using jQuery with less code

$("#state").change(function(){  
  $("#first, #second").prop("disabled", $(":selected",this).length < 2);
});

 $("#state").change(function(){ $("#first, #second").prop("disabled", $(":selected",this).length < 2); }); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <div class="form-group mb-3"> <select class="selectpicker show-tick decore" name="state" id="state" multiple> <option value="one">one</option> <option value="two">two</option> </select> </div> <div class="input-group mb-3"> <div class="input-group-prepend"> <span class="input-group-text" id="basic-addon1"> <i class="fas fa-child"></i> </span> </div> <input type="text" name="first" id="first" class="form-control" placeholder="first" aria-label="first" aria-describedby="basic-addon1" disabled /> <input type="text" name="second" id="second" class="form-control" placeholder="second" aria-label="second" aria-describedby="basic-addon1" disabled /> </div>