JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<form>
  <div><input type="text" class="class_name" /></div>  
  <div><input type="text" class="class_name" /></div>
  <div><input type="text" class="class_name" /></div>
  <div><input type="text" class="class_name" /></div>
  
  <input type="submit" value="Go" />
</form>
<p>
</p>

JavaScript

function checkDuplicates() {
  // get all input elements
  var $elems = $('.class_name');

  // we store the inputs value inside this array
  var values = [];
  // return this
  var isDuplicated = false;
  // loop through elements
  $elems.each(function () {
    //If value is empty then move to the next iteration.
    if(!this.value) return true;
    //If the stored array has this value, break from the each method
    if(values.indexOf(this.value) !== -1) {
       isDuplicated = true;
       return false;
     }
    // store the value
    values.push(this.value);
  });   
 
return isDuplicated;     
}

$('input[type=submit]').on('click', function(e) {
e.preventDefault();
if(checkDuplicates())
 $('p').html('Has duplication');
 else  $('p').html('No duplication');
})