JSFiddle - React, Tailwind, and code Playground
HTML
<div><label>Longitude<br/><input id=longitude name=longitude /></label></div>
<div><label>Longitude (degrees)<br/><input id=longitude_deg name=longitude_deg /></label></div>°
JavaScript
$('#longitude_deg').on('keypress', function(e) {
if(e.keyCode === 32) {
this.value += '° ';
}
})
.on('change', function() {
$('#longitude').val(this.value);
});