React Prop Validation for Date Strings

You can basically copy-paste from prop-types documentation using a proper regex:

yourProp: function(props, propName, componentName) {
  if (!/\d{4}\/\d{2}\/\d{2}/.test(props[propName])) {
    return new Error(
      'Invalid prop `' + propName + '` supplied to' +
      ' `' + componentName + '`. Validation failed.'
    );
  }
}

Remember, the documentation is your friend: https://www.npmjs.com/package/prop-types