JSFiddle - React, Tailwind, and code Playground

HTML

<input value="111"> //similar
<input value="222">
<input value="111"> //similar
<input value="333">

JavaScript

var vals = {};
    
    $('input').each(function() {
        var index = $(this).val();
        if (vals[index])
        {
            vals[index]++
        }
        else
        { 
            vals[index] = 1;
        }
    });
    
    var duplicates = $.map(vals, function(val, key){
        return (val > 1) ? key : null;
    });

    if (duplicates.length > 0) alert('There are duplicates!');