JavaScript Array.toSentence - inspired by Ruby's Array#to_sentence

index.js

// Transforms an array into a sentence.
// Example:
//     toSentence(['apples', 'oranges', 'melons']);
//     >> "apples, oranges and melons."
export function toSentence(arr) {
  if (arr.length === 0) return '';

  return arr.length > 1
    ? `${arr.slice(0, arr.length - 1).join(', ')} and ${arr.slice(-1)}.`
    : `${arr[0]}.`;
}

test.js

describe('toSentence', () => {
  it('joins an array into a comma-separated string, ending with a dot', () => {
    expect(toSentence([])).to.eq('');
    expect(toSentence(['dog'])).to.eq('dog.');
    expect(toSentence(['foo', 'bar', 'baz'])).to.eq('foo, bar and baz.');
  });
});