JSFiddle - React, Tailwind, and code Playground

HTML

<select name="g1" id="box_g1">
	<option value="Select">Select</option>
	<option value="one">one</option>
	<option value="two">two</option>
	<option value="three">three</option>
</select>

<select name="g2" id="box_g2">
<option value="Select">Select</option>
	<option value="one">one</option>
	<option value="two">two</option>
	<option value="three">three</option>
</select>

<select name="g3" id="box_g3">
<option value="Select">Select</option>
	<option value="one">one</option>
	<option value="two">two</option>
	<option value="three">three</option>
</select>

JavaScript

var g1 = [],
        g2 = [];
    $('#box_g1 option').each(function(){g1.push($(this).val());});
    $('#box_g2 option').each(function(){g2.push($(this).val());});

    $('#box_g1').on('change', function(){
        var options = '',
            selected = $('#box_g1').val();
        for(var i = 0; i < g2.length; i++){
            if(selected != g1[i] && selected != 'Select'){
                options += ('<option value="'+g2[i]+'">'+g2[i]+'</option>');
            }
        }
        $('#box_g2').empty().html(options);
    });