decapitalize

Decapitalizes the first letter of a string.

Use array destructuring and String.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 parameter 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'