JSFiddle - React, Tailwind, and code Playground

HTML

<select id="country">
  <option value="USA">United States</option>
  <option value="Ind">India</option>
  <option value="NZ" selected>New Zealand</option> 
    <option value="NZ" >New Zealand</option>
  <option value="SA">South Africa</option>
  <option value="UK">United Kingdom</option>
    <option value="UK">United Kingdom</option>
 <option value="JP">Japan</option>
</select>

JavaScript

[].slice.call(country.options)
  .map(function(a){
    if(this[a.innerText]){ 
      country.removeChild(a); 
    } else { 
      this[a.innerText]=1; 
    } 
  },{});