Below are the ways to get the value from all types of form elements.
In all cases, the form is called That's checking the value's equality with a null String (two single quotes with nothing between them).
At first we use regular expression and the replace() method to clear out any spacer characters.
Next, we use the is Na N() function to check if the phone number contain only numbers.
Also, the @ must not be the first character of the email address, and the last dot must at least be one character after the @ sign.
At first we check if the user entered anything at all in the email field.
If its not blank, the function returns an empty string.
validate Username ( ) The function below checks if the user entered anything at all in the username field.
Otherwise it returns a message describing the error and highlight appropriate element with yellow.validate Email ( ) Next we want to see if the email address the user entered is real.This means that the input data must contain at least an @ sign and a dot (.).For the majority of your users, Java Script form validation will save a lot of time up front, but double-checking the data on the server remains necessary, in case the user has turned Java Script off.Form data that typically are checked by a Java Script could be: validate Form On Submit ( ) This is a main function that calls a series of subfunctions, each of which checks a single form element for compliance.