new StringBuilder(hi).reverse().toString()

const luhnCheck = num => {
  let arr = (num + '')
    .split('')
    .reverse()
    .map(x => parseInt(x));
  let lastDigit = arr.splice(0, 1)[0];
  let sum = arr.reduce(
    (acc, val, i) => (i % 2 !== 0 ? acc + val : acc + ((val *= 2) > 9 ? val - 9 : val)),
    0
  );
  sum += lastDigit;
  return sum % 10 === 0;
};

luhnCheck('4485275742308327'); // true
luhnCheck(6011329933655299); //  true
luhnCheck(123456789); // false

// `date` is a `Date` object
const formatYmd = date => date.toISOString().slice(0, 10);

// Example
formatYmd(new Date());      // 2020-05-06

function Welcome(props) {
  return <h1>Hello, {props.name}</h1>;
}

function App() {
  return (
    <div>
      <Welcome name="Sara" />
      <Welcome name="Cahal" />
      <Welcome name="Edite" />
    </div>
  );
}

ReactDOM.render(
  <App />,
  document.getElementById('root')
);

// `arr` is an array
const clone = arr => arr.slice(0);

// Or
const clone = arr => [...arr];

// Or
const clone = arr => Array.from(arr);

// Or
const clone = arr => arr.map(x => x);

// Or
const clone = arr => JSON.parse(JSON.stringify(arr));

// Or
const clone = arr => arr.concat([]);

<div className="md:self-start sticky top-16 bg-background px-4 mt-1 sm:px-6 md:pt-4 lg:pl-8 lg:pr-4">
          <ScrollArea className="whitespace-nowrap">
            <div className="w-max flex md:flex-col gap-1 bg-transparent text-muted-foreground pb-2">
              {menuData.map((section) => (
                <Button
                  key={section.title}
                  onClick={() => handleScrollToSection(section.title)}
                  variant="ghost"
                  size="sm"
                  className={cn(
                    'w-auto md:w-full hover:cursor-pointer relative md:justify-end',
                    activeSection === section.title
                      ? cn(
                          'text-foreground after:absolute after:bottom-[-2px] after:bottom-0 after:w-full after:h-[2px] after:bg-primary',
                          'md:after:right-[-2px] md:after:top-0 md:after:h-full md:after:w-[2px]',
                        )
                      : '',
                  )}
                >
                  {section.title}
                </Button>
              ))}
            </div>
            <ScrollBar orientation="horizontal" />
          </ScrollArea>
        </div>