JSFiddle - React, Tailwind, and code Playground

by mainerror

HTML

<label for="agecb"> Show age field:
    <input id="agecb" type="checkbox" name="agecb" />
</label>
<input id="age" type="text" name="age" placeholder="Enter your age" hidden/>

CSS

label {
    display: block;
}

JavaScript

var ageCheckbox = document.getElementById('agecb');
var ageInput = document.getElementById('age');

// Just because of IE <333
ageCheckbox.onchange = function() {
    // Check if the checkbox is checked, and show/hide the text field.
    ageInput.hidden = this.checked ? false : true;
};