JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
<button data-direction="increase">increase</button>
<button data-direction="decrease">decrease</button>
<input value="1.0" />

JavaScript

$(function() {
	var button = $('button');
  
  button.click(function() {
  	var button = $(this);
  	var direction = button.data('direction');
    
    var input = $('input');
    var current_value = parseFloat( input.val() ).toFixed(1);
    
    var new_value;
    
    if (direction=='increase') {
	    new_value = current_value + 0.1;
    } else {
	    new_value = current_value - 0.1;    
    }
    
    input.val(new_value);
  
  });

});