JSFiddle - React, Tailwind, and code Playground
JavaScript
var s = "#ff0000";
var patt = /^#([\da-fA-F]{2})([\da-fA-F]{2})([\da-fA-F]{2})$/;
var matches = patt.exec(s);
var rgb = "rgb("+parseInt(matches[1], 16)+","+parseInt(matches[2], 16)+","+parseInt(matches[3], 16)+");";
alert(rgb);