Decapitalizes the first letter of a string.

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


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


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