JavaScript: validate forms with Regular Expressions (RegEx)

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I know I've been posting a lot on forms and validation recently, however we should all agree on the fact that form validation is really a serious problem for programmers.

When a user submit data to our database, the first thing we should consider is to protect the destination. Our database is waiting for specific data and, for example, a text string must not be submitted to a smalldate field.
On the other hand, we should provide a complete and efficient way to help the user in filling in the form. Specifically in commercial situations, if we want the visitors to conclude painlessly a commercial transaction, we should make things the easiest possible way for him/her.

When we check what the user is submitting, we can be sure that the birth date or the credit card expiration date is truly a valid date - for the user protection and security and for the web site owner who needs to be sure that everything works smoothly.

In the following example, we are going to validate emails, however, by changing the regular expression, we can check almost anything.
In the following example we use RegEx in a short JavaScript function.

HTML: HTML5 new input types

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HTML5 introduced some new input types with better control and validation. When the features will be completely supported by all main browsers, creating forms will surely be easier and faster.
The new types are:

• email;
• url;
• number;
• range;
• dates;
• color.

As you can see they are quite interesting. Let's take a tour and see how they work.

ASP: how to create effective date fields for forms

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Today we are going to create a date field for a form. The goal is to make it beautiful to see, easy to use and with validation. We are going to use ASP and just a touch of CSS.
The form element will look like:

Day 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Month 01 02 03 04 05 06 07 08 09 10 11 12 Year 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

In the example above, I have inserted all the options manually, but as I will show you, we are going to make the values of the three option controls automatic. - Note that if you are reading this post via your RSS reader you might not see the above example in the way it was meant.

Ok. Let's start with the code.

ASP: simple form validation

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Form validation is an important element in every web site. In order to be sure that the user submits data in accordance to what our code (or backend database) is expecting, it is mandatory to check the information before doing anything else.
There are tons of ready-made form validation functions on the web, especially written in JavaScript, however sometimes we might need to do something a little bit more customized.
Here I will explain the basic concept behind a form validation using VBScript in an ASP page.

ASP: is this a date? The IsDate function

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Form validation is probably the most wanted feature by web developers. Every web programmer, at least once in a lifetime, has dealt with the issue: the user fills in the form and submit wrong data. Without validation, the best thing could happen is that an error is thrown. The worst case? The wrong data is submitted to your database... and believe me, most of the time you don't want that.
While complete JavaScript form validation solutions are available everywhere, today I would like to point out that VBScript has a very simple function that can help us in checking dates at least.

The function

The function I am talking about is IsDate. I've already talked about the function in a post about SQL Server queries and date functions. The VBScript function works in a similar way.
Basically it returns a Boolean value (true/false) stating if an expression is a date or can be converted to a date. The function uses the local settings in the evaluation process, so be careful in using it: for example, English months in words are not the same in Italian.