JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" value="1,000" id="input_one" size="10" />
&nbsp;<strong>+</strong>&nbsp;
<input type="text" value="1,000" id="input_two" size="10" />
&nbsp;<strong>=</strong>&nbsp;
<input type="text" value="2,000" id="sum" size="10" />&nbsp;
<input type="button" id="submit" value="Add it!" />

JavaScript

$("#submit").click( function() {
    var value_one = $("#input_one").val();
    var value_two = $("#input_two").val();
    
    var value_one_int = parseInt( $("#input_one").val().replace(',', ''), 10 );
    var value_two_int = parseInt( $("#input_two").val().replace(',', ''), 10 );
    
    var sum = value_one_int + value_two_int;
    
    $("#sum").val( addCommas(sum) );
});

function addCommas(nStr)
{
	nStr += '';
	x = nStr.split('.');
	x1 = x[0];
	x2 = x.length > 1 ? '.' + x[1] : '';
	var rgx = /(\d+)(\d{3})/;
	while (rgx.test(x1)) {
		x1 = x1.replace(rgx, '$1' + ',' + '$2');
	}
	return x1 + x2;
}