JSFiddle - React, Tailwind, and code Playground

HTML

<input class="input_name" value="bert" />
<input class="input_name" value="king kong" />
<input class="input_name" value="john" />
<input class="input_name" value="john" />

JavaScript

$(".radio .new_input").bind("blur",function(){
    if (findDuplicate($(this).val()) == 1){
    	$(this).after('<p class="option-exist" style="color:red">This option already exist.</p>');
    }else{
    	$(this).parent().find($('.option-exist').remove());
    }
})

function findDuplicate(value){
    var result = $(".radio .new_input[value='" + value + "']").length - 1;
    return result;
}