decapitalize

Decapitalizes the first letter of a string.

• Use array destructuring and String.prototype.toLowerCase() to decapitalize first letter, ...rest to get array of characters after first letter and then Array.prototype.join('') to make it a string again.
• Omit the upperRest argument to keep the rest of the string intact, or set it to true to convert to uppercase.

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

decapitalize('FooBar'); // 'fooBar'
decapitalize('FooBar', true); // 'fOOBAR'