How to implement JavaScript form validation and E-mail validation

This article is about how JavaScript form validation and E-mail validation are implemented. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

JavaScript form validation

JavaScript can be used to validate the input data in the HTML form before it is sent to the server.

These typical form data validated by JavaScript are:

Has the user completed the required items in the form?

Is the email address entered by the user legal?

Has the user entered a valid date?

Did the user enter text in the data field (numeric field)?

Required (or required) items

The following function is used to check whether the user has filled in the required (or required) items in the form.

If the required or required option is empty, the warning box pops up and the return value of the function is false:

Function validate_required (field,alerttxt) {with (field) {if (value==null | | value== "") {alert (alerttxt); return false} else {return true}

Here is the code along with the HTML form:

Function validate_required (field,alerttxt) {with (field) {if (value==null | | value== ") {alert (alerttxt); return false} else {return true} function validate_form (thisform) {with (thisform) {if (validate_required (email," Email must be filled out! ") = = false) {email.focus (); return false}