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Submitting forms conditionally using JavaScript

In the long-gone days of the early Internet, having a form on the
website was tantamount to dabbling with "cutting-edge" technologies.
Intricate Perl scripts and esoteric CGI scripts were required to
process those forms and people used to suffer bouts of cold sweat
whenever there manifested a need to use web forms. To create a
form-handling script used to be in the realms of MCAs and computer
engineers. No longer is it so. The Internet these days is replete with
all sorts of form handling scripts, and wherever you choose to host
your website, or for that matter even a web page, you can easily deploy
a form handling script and start interacting with your visitors.

As the level of interaction goes complex, you require more complicated
scripts. One way is to write a single script containing hundreds of
lines of code. The action script (that comes within <form …
action="scriptname.php">) encompasses numerous if-then-else
conditions, and even within these conditions, there could be zillions
of nested if-then-else conditions. After a certain time it becomes a
Herculean task to maintain such a form handling script and unless you
are an avid documenter, you’ll lose the track in no time.

The second way is, write smaller scripts and let the form call them
according to the user input. This can save you hundreds of lines of
coding, and even if it doesn’t, it makes things a lot easier. Suppose
you have a form that, along with other things, asks the visitor to
which state she belongs. Then, when she clicks the submit button, the
action happens according the state she selected. If you have a single
script and if you want the script to act according to the individual
state, you might end up writing a very large action script. On the
other hand, if you specifically write a script for, let us say,
California; then you have to write code only centered around California
and you can, for the time being, forget about other states.

Javascript lets you submit a single form, conditionally, to different
script. Here, we’ll learn how to achieve this. First, let us go through
a simple form:

<form method="post" name="frm1" onSubmit="javascript: decide_action();" action="">
<input type="radio" name="ch" value="one" /> Choice 1
<input type="radio" name="ch" value="two" /> Choice 2
<input type="radio" name="ch" value="three" /> Choice 3
<input type="submit" name="s1" value="Submit" />
</form>

As you can see, this form displays three radio buttons. The objective
is, send the form to a script according to the radio button selected.
Since some Javascript action needs to take place once the Submit button
is clicked, we invoke decide_action() function through the onSubmit
attribute of the <form> tag. Although we include the action
attribute, it is left blank. The other form fields are the usual ones.
Now let us dive into the cryptic world of the actual script that steers
the submission.

<script language="javascript">

function decide_action()
{
if(check_buttons()==true)
{
if(document.frm1.ch[0].checked==true)
{
document.frm1.action="one.php";
}
else if(document.frm1.ch[1].checked==true)
{
document.frm1.action="two.php";
}
else
{
document.frm1.action="three.php";
}
document.frm1.submit();
}
}

function check_buttons()
{
var ok=false;
for(i=0; i<3; i++)
{
if(document.frm1.ch[i].checked==true)
{
ok=true;
}
}
if(ok==false)
{
alert("Select at least one option.");
}
return ok;
}

</script>

This script contains two functions. The latter one, check_buttons(),
makes sure that you select at least one option because if you don’t
select an option, Javascript doesn’t know which form handling script to
invoke. It first initializes a variable, ok, to false:

var ok=false;

then through a loop it checks all the radio buttons of the form. As
soon as it encounters a radio button that is checked, it assigns the
value true to ok

ok=true;

When the function, decide_action() encounters a true:

if(check_buttons()==true)

it first assigns a file name to the action attribute of the object frm1 (the name of the form):

document.frm1.action=file_name;

and then calls the submit() function for that form:

document.frm1.submit();

The script uses multiple if-else decisions to check which radio button
was selected, and then submits the form to a form handling script
accordingly.

Now, let us take both the functions: check_buttons() and
decide_action() to the next level. There can be varied number of radio
buttons to check. Why just limit to three radio buttons. The following
code not only handles limitless radio buttons, it also assigns the name
of the file accordingly (the value of the radio button should be the
name of the respective action file).

<script language="javascript">

function decide_action()
{
var file_destination=check_buttons();

if(file_destination!="")
{
document.frm1.action=file_destination + ".php";
document.frm1.submit();
}
}

function check_buttons()
{
var val="";
for(i=0; i<document.frm1.ch.length; i++)
{
if(document.frm1.ch[i].checked==true)
{
val=document.frm1.ch[i].value;
}
}
if(val=="")
{
alert("Select at least one option.");
}
return val;
}
</script>

This next version of the code is much smaller as it gets rid of
multiple if-else statements. Since a particular set of radio buttons is
actually an array, we can loop through the array to find out which
button is checked. Then we can store the value stored at that index
location and return it to the calling function — decide_action().
decide_action() this time uses the value returned, appends the
extension ".php", assigns it to the action attribute and then submits
it.

This article has walked you through various concepts, but mainly,
submitting form to different scripts according to selections made in
the form.