JSFiddle - React, Tailwind, and code Playground

HTML

<input id="textfield" name="textfield" type="text" placeholder="enter something" />

<input id="textfield" name="textfield" type="text" data-placeholder="enter something">

JavaScript

var inputs = document.getElementsByTagName("input");
for (var i = 0; i < inputs.length; i++) {
    inputs[i].value = inputs[i].getAttribute('data-placeholder');
    inputs[i].addEventListener('focus', function() {
        if (this.value == this.getAttribute('data-placeholder')) {
            this.value = '';
        }
    });
    inputs[i].addEventListener('blur', function() {
        if (this.value == '') {
            this.value = this.getAttribute('data-placeholder');
        }
    });
}