JSFiddle - React, Tailwind, and code Playground

HTML

Number:
<input type="number" id="myNumber">
<button class="increment-button" data-target="#myNumber">+</button>


Number:
<input type="number" id="myNumber2">
<button class="increment-button" data-target="#myNumber2">+</button>

JavaScript

var buttons = document.querySelectorAll('.increment-button');

// we have to borrow 'forEach' method from Array, 
// as NodeList doesn't have that method
Array.prototype.forEach.call(buttons, function(button) {
  var inputSelector = button.getAttribute('data-target');
  var input = document.querySelector(inputSelector);

	button.addEventListener('click', function() {
  	input.stepUp(1);
  });
});