'@' symbol and a period
'.', nothing more!
validateEmila function relies on the global method
indexOf. That method returns the first position at which the specified string value occurs.
Keep in mind that this is not a complete and exhaustive method of validating an email address. There are better and more comprehensive ways to do so. For example, make sure that the email address doesn’t contain any spaces, symbols, HTML characters, or that it starts with a letter, not a digit.