JSFiddle - React, Tailwind, and code Playground
HTML
<script>
alert(( new Date("1970-1-1 12:42 ") - new Date("1970-1-1 9:42") ) / 1000 / 60 / 60 );</script>
<script>
alert(( new Date("1970-1-1 12:42 ") - new Date("1970-1-1 9:42") ) / 1000 / 60 / 60 );</script>