JSFiddle - React, Tailwind, and code Playground

HTML

<select class="check" name="first">
        <option value="">Select</option>
        <option value="some" required="true">Some required</option>
        <option value="other">Other Value</option>
        <option value="few" required="true">Few required</option>
    </select>
    <select class="check" name="second">
        <option value="">Select</option>
        <option value="some" required="true">Some required</option>
        <option value="other">Other Value</option>
        <option value="few" required="true">Few required</option>
    </select>
    <select class="check" name="third">
        <option value="">Select</option>
        <option value="some" required="true">Some required</option>
        <option value="other">Other Value</option>
        <option value="few" required="true">Few required</option>
    </select>
    <select name="other">
        <option value="">Select</option>
        <option value="some" required="true">Some required</option>
        <option value="other">Other Value</option>
        <option value="few" required="true">Few required</option>
    </select>

<button class="check-select">Check!</button>

JavaScript

$(document).on('click','.check-select',function(){
    var requiredFields = array();
    $('option:selected', this).attr('required').each(function(){
        requiredFields[]=$(this).val();
    })

    var valuesSelected = array();
    $('.check').each(function(){
        valuesSelected[]=$(this).val();
    })

    for(i=0;i<requiredFields;i++){
        if(jQuery.inArray(requiredFields[i], valuesSelected)==-1){
             var error += 'Please select '+requiredFields[i];
        }
    }

    if(error!=''){
        alert(error); // just for testing
    } else {
         // have fun
    }
});