alert("Please enter a valid email address");
Form validation of the pattern if(myTextField.value == ") is barely worthy of the name, and virtually useless, as even a single space, an X or a ? will return false, that is pass the validation. Numeric values, such as zip codes and phone numbers, should be validated as such. Ditto email addresses. This topic has been covered many times before in this forum.
In the first book of the Bible, Guinness, God got tired of creating the world so he took the Sabbath off. - Pupil's answer to Catholic Elementary School test.
All the code given in this post has been tested and is intended to address the question asked.
Unless stated otherwise it is not just a demonstration.