Validating Form Input in JavaScript by Amrit Hallan
This time we'll make a form that collects information about the visitor at your
site. You must have filled-in copious registration forms or survey forms where
you had to enter your name, your email, your address, etc. Sometimes users,
intentionally or unintentionally, enter wrong information that can either spoil
your database scheme or give you lots of useless data and hence, waste your
precious server space.
To avoid such problems, as much as it can be managed, we programmatically try
to make sure, that data is entered in an orderly fashion, and no unusable
fields are entered. Checking individual fields of the form does this.
We'll see a form here with three fields: Name, Phone and Email. In this form,
no field should be left blank, there should be no numbers in the Name field
[1,2,3,4,.], and in the Email field, no email should be without the "@" sign.
We can carry out more complex validations, but at the moment, these three
should suffice.
/// Remove the extra dots while testing. They have been just inserted so that
some email programs don't freak out at the presence of a JavaScript in the
email.
<..script language="JavaScript1.2"> function CheckName(HoldName) {
NoNumThere='true'; for(i=0; i<HoldName.length; i++) { for(j=0; j<10; j++)
{ if(HoldName.charAt(i)==j.toString()) { NoNumThere='false'; break; } }
if(NoNumThere=='false') { break; } } return NoNumThere; } function
CheckMail(HoldMail) { IsValid='true'; if(HoldMail.indexOf("@")<=0) {
IsValid='false'; } return IsValid; } function checkfields() { var
AllFilled='true'; for(i=0; i<3; i++) {
if(visitor.elements[i].value.length==0) { alert("The field [" +
visitor.elements[i].name + "] can not be left blank."); AllFilled='false';
visitor.elements[i].focus; return; } } if(AllFilled=='true') { var
NameValid=true; var EmailValid=true; NameValid=CheckName(visitor.vname.value);
EmailValid=CheckMail(visitor.vemail.value); if(NameValid=='false') {
alert("Sorry, your name can not contain numbers."); visitor.vname.focus; }
if(EmailValid=='false') { alert("Sorry, this does not seem like a valid email
address."); } } if(NameValid=='true' & EmailValid=='true') {
alert("RIGHTO!!!"); } } </script> <body> <form
name="visitor"> Enter your name: <input name="vname" type="Text">
Enter you phone: <input name="vphone" type="Text">
Enter your email: <input name="vemail" type="Text">
<input type="Button" name="submit" value="Submit"
onclick="checkfields();"> <input type="Reset" name="reset"
value="Reset"> </form>
</body> </html>
Copy and paste the code as it is, and save the entire content as a new HTML
page. Then load it on to your browser. Unless you see the result, it'll be
difficult to follow the script if you do not have prior programming background.
The first condition is, none of the fields can be submitted blank. Click on the
submit button without entering anything and observe the reaction.
Here, we are making ample use of the recently learnt for(){.} loop. Then we
have used function too, to carry out certain validations. Our main function,
checkfields(), is associated with the OnClick attribute of the "Submit" button,
that is, when you click on the "Submit" button, this function gets triggered.
Some new terms in today's script are: true, false, charAt(), toString(), break,
indexOf(), string.length, and orm.elements[ ].
A quick explanation to make things easier:
If at 10:30 pm, I say, "It is night", then
var fact='true'
and if I say at 10:30 pm that "It's afternoon", then
var fact='false'
Which explains the use of true and false, which are also called Boolean
operators, which means, a Boolean variable can either be true or false, but
NEVER both.
Until we learn about arrays, every character in a string has an index position.
For instance, if we have
var city="Delhi"
then city.charAt(0)="D", city.charAt(1)="e",
city.charAt(2)="l"...city.charAt(4)="i".
toString(), converts another data type to a string data-type. For example,
var num1=31 var num2=21 var char1=num1.toString() var char2=num2.toString()
So,
num1+num2=52 and char1+char2=3221
In the second case, instead of being added, the variables are being
concatenated, which indicates that they are strings, not numbers. We'll see its
application later.
break, true to its name, breaks something. In this case, it breaks the loop in
which it occurs, and takes the execution of the program to the line immediately
after the loop, without meeting the condition required to complete the loop.
indexOf() tells us about the position of a particular character in a string.
Look its use in the following code:
var city="Delhi"
Referring to this code, city.indexOf("e") should give us a value 1 and
city.indexOf("h") should give us a value 3. city.indexOf("z") should give us a
value less than zero, indicating that it does not belong to the given string.
String.length gives us the length of the string, for instance, if city="Delhi",
then city.length would give us 5.
Again, elements[ ] is an array, and we haven't dealt with them yet, so we leave
the rest of the explanation to the next section.
About the Author
Amrit Hallan is a freelance web designer. For all web site development and web
promotion needs, you can get in touch with him at amrit@bytesworth.com or
http://www.bytesworth.com. For more such articles, visit
http://www.bytesworth.com/articles You can subscribe to his newsletter
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