[Javascript] server-side:client-side workload ratio

[Paul Novitski]

Dave,

Good points.  When I duplicate input validation on the client side, it's 
mainly for the user's benefit -- so they don't have to wait for a form 
submit & return just to find out they made a typo or left a field 
blank.  Fundamentally it's the server-side script's responsibility to 
validate all incoming data.

In my original posting I focused on page download, not form response, but 
what you say fits in with the general direction I seem to be heading -- 
dividing an application into two faces, with the server-side script 
handling interaction with databases, web services, and other connectable 
resources, and the client-side script handling interaction with the human 
user.  On the surface that may seem like an inane tautology, but with 
client-side scripts that can see and manipulate the DOM, just where to 
separate various aspects of page rendering is what I'm wrestling with in 
trying to devise my programming policies.

Wanting to accommodate browsers that have disabled client-side scripting is 
a pretty good reason to amend my prior example -- not to download mere data 
arrays for the client-side script to format into a table, but instead to 
download the data in an HTML table that works in some rudimentary way even 
in the absence of Javascript.

You said:
>My litmus test is that any or all information which may still yet be edited
>by the user PRIOR to submission is handled by client-side scripting, and
>anything else is handled by server-side scripting -- including final
>validation for fields.

This feels like too sweeping a statement for me.  I often process data 
before downloading it to the client, things such as pre-validating fields, 
reformatting them, splitting a date/time field into two separate fields, 
maybe supplying listbox options for certain fields, perhaps concatenating 
first & last name, that sort of thing.  To me it feels like the 
server-script's responsibility to deliver data to the client that's ready 
to view or edit, and the client's responsibility to handle fine details of 
display style and user interaction, including primary validation.  Do you 
ever download raw data and do all your reformatting it in Javascript before 
presenting it to the user in display or input fields?  Or only in certain 
cases?  I'm curious.

Cheers,
Paul


At 04:40 PM 3/21/2004, you wrote:
>Typically, those scripts which access things resident on the server (like
>database information, files in shared distribution libraries, etc.) are done
>with server-side scripting -- even when (by some highly questionable and
>tortuous methods) client-side Javascript could be finagled into doing the
>same thing.  Remember -- anything on a client machine must and should be
>regarded as suspect, tampered with, eavesdropped upon, and generally nasty.
>Piping it directly into the server application without vetting it first is
>not a recommended process.
>
>Also, it is important to split the validation process so that everything
>which MUST be validated on a form submission is done on the server-side.
>This is done in the instance that the client has disabled Javascript on the
>browser, either accidently or deliberately.
>
>My litmus test is that any or all information which may still yet be edited
>by the user PRIOR to submission is handled by client-side scripting, and
>anything else is handled by server-side scripting -- including final
>validation for fields.
>
>At least that's my take on the subject.
>
>-- Dave Lovering
>
>----- Original Message -----
>From: "Innerlab" <innerlab at hotmail.com>
>To: "[JavaScript List]" <javascript at LaTech.edu>
>Sent: Sunday, March 21, 2004 1:31 PM
>Subject: Re: [Javascript] server-side:client-side workload ratio
>
>
> > Interesting thread. I look forward to read more.
> > I am not an expert, so I don't think I can contribute much.
> >
> >
> > ----- Original Message -----
> > From: "Paul Novitski" <paul at dandemutande.org>
> > To: "[JavaScript List]" <javascript at LaTech.edu>
> > Sent: Sunday, March 21, 2004 1:51 PM
> > Subject: [Javascript] server-side:client-side workload ratio
> >
> >
> > > Friends,
> > >
> > > As my client-side scripts become capable of performing more complex
>tasks,
> > > I'm left wondering how I should split the workload between my
>server-side
> > > scripts and my client-side scripts.  What fundamental characteristics of
> > > the page-rendering process naturally argue for placement above or
> > > below?  If you've given this some thought and have come up with some
> > > conclusions that work for you, please share them.
> > >
> > > (For this musing I'm considering "hand-crafted" scripts such as
>VBscript,
> > > PHP, and Javascript, bypassing the .Net programming environment that can
> > > handle most of the server/client side issues as one integrated process.)
> > >
> > > My initial inclination is to give server-side scripts most of the
> > > application-specific work and give client-side scripts more generic
>tasks
> > > that I can re-use more often, although I don't have a rigorous argument
> > for
> > > that yet.
> > >
> > > One area that seems clear concerns download time.  Especially in a era
> > when
> > > so many users are on slow connections, it would behoove us to minimize
>the
> > > size of downloaded pages without sacrificing the complexity of the user
> > > interface.
> > >
> > > Consider an application that reads a dataset and downloads it to the
> > > browser for display or editing.  The data need to be massaged before
> > > presentation in the browser: some fields made into hyperlinks, others
> > > reformatted, concatenated, or converted for user friendliness.
> > >
> > > Because it's the server-side script's responsibility to read the dataset
> > in
> > > the first place, I'm inclined to give it the job of initial
>reformatting:
> > > - selected the desired columns;
> > > - performing the initial record sort;
> > > - performing data conversions (enforcing date & time formats, replacing
> > > code values with human language words, concatenating fields, etc.);
> > >
> > > ... and give the client-side script the work that pertains to the
>details
> > > of the user interface:
> > > - assigning CSS classes & styles;
> > > - assigning GUI events & hyperlinks;
> > > - inserting the data grid in the page and organizing its structure, e.g.
> > > separating the field name row from the data rows to enable a scrolling
> > > dataset with fixed heads.
> > >
> > > For fast response time, I'm inclined to keep the size of the downloaded
> > > page small and add any necessary redundant bulk with the client-side
> > > script.  For instance, the server-side script could dictate the CSS
> > classes
> > > of each data column in a single row, and the client-side script could
> > > assign these to every data row in body onLoad(), resulting in a slim
> > > download and a fat result.
> > >
> > > The server-side script could generate Javascript such as:
> > >
> > > var aFieldNames = new Array("Date","Contact","Email");
> > > var aRowClasses = new Array("cssFldDate","cssFldContact","cssFldEmail");
> > > var aRowLinkTypes = new Array("","","mailto");
> > > var aDataset = new Array();
> > > aDataset[0] = new Array("03/01/2004","Jo Blo","joblo at thingie.com");
> > > aDataset[1] = new Array("03/04/2004","Sam Sham","samsham at froggie.org");
> > > ...
> > >
> > > Javascript could build the actual data grid structure (using table or
> > > layers) and assign classes, link structures, and mouse events to each
>cell
> > > of the dataset as it builds them, ultimately generating a structure much
> > > wordier than the essential information that's been downloaded.
> > >
> > > Any further thoughts anyone has on this topic would be appreciated.
> > >
> > > Paul
> > >
> > >
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