JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" name="test" placeholder="testing">
<button id="btn-hide" onclick="togglePlaceholder(false)">Hide</button>
<button id="btn-show" onclick="togglePlaceholder(true)">Show</button>

JavaScript

function togglePlaceholder(show) {
	var tb = document.getElementByName('test');
  alert(tb);
  if (!show) {
  	tb.placeholder = '';
  }
  else {
  	tb.placeholder = 'testing';
  }
}