JSFiddle - React, Tailwind, and code Playground

JavaScript

function camelToSpace(str) {
    //Add space on all uppercase letters
    var result = str.replace(/([A-Z])/g, ' $1').toLowerCase();
    //Trim leading and trailing spaces
    result = result.trim();
    //Uppercase first letter
    return result.charAt(0).toUpperCase() + result.slice(1);
}

alert(camelToSpace("thisIsAPain"));