capitalize

Capitalizes the first letter of a string.

• Use array destructuring and String.prototype.toUpperCase() to capitalize the first letter of the string.
• Use Array.prototype.join('') to combine the capitalized first with the ...rest of the characters.
• Omit the lowerRest argument to keep the rest of the string intact, or set it to true to convert to lowercase.

const capitalize = ([first, ...rest], lowerRest = false) =>
  first.toUpperCase() +
  (lowerRest ? rest.join('').toLowerCase() : rest.join(''));

capitalize('fooBar'); // 'FooBar'
capitalize('fooBar', true); // 'Foobar'