function to capitalize text

capitalize.js

// string.js
export const capitalize = (string = '') =>
  (typeof string === 'string' && string.substring(1))
    ? string[0].toUpperCase() + string.substring(1).toLowerCase()
    : '';

// string.test.js
import { capitalize } from './string';


describe('[Helpers] string', () => {
  describe('capitalize()', () => {
    it('should return string Capitalized', () => {
      expect(capitalize()).toEqual('');
      expect(capitalize('')).toEqual('');
      expect(capitalize('foo')).toEqual('Foo');
      expect(capitalize('fOO')).toEqual('Foo');
      expect(capitalize(0)).toEqual('');
      expect(capitalize(1)).toEqual('');
      expect(capitalize(true)).toEqual('');
      expect(capitalize(false)).toEqual('');
      expect(capitalize('foo bar')).toEqual('Foo bar');
    });
  });
});