Controlling Javascript from server side

[akineko]

Hi everyone,

First of all, I'm not an expert on Javascript. Please forgive me if my
question is pointless.

I want control a hardware device using a Web browser.
I created a page which has a form containing all necessary INPUTs.
By clicking a button, all current settings are sent to the server side
(using POST or GET) so that the server can interact with the hardware,
which is under the server's control.

Now, in some cases, I want to update the INPUT (w/ readonly) with the
data from the hardware, such as a status value.
Most primitive approach is creating a new page with new value to the
INPUT, where I want to show the value.

But that is not quite efficient as the page appearance won't change
except the contents of the INPUT.

As Javascript can make any change to the HTML page (at client's side)
that is currently being displayed, it is more straight forward if the
server can send a set of Javascript commands to the web server so that
it can just update the display contents rather than refreshing
everything.

I thought such scheme was already available, but so far, I don't see
anything usable.
The Web server is not a commercial one but a custom Web server
(written in Python) so that I want to keep the scheme as simple as
possible. I checked AJAX but I'm not sure I can use AJAX in my
application.

Any suggestion will be greatly appreciated.

Best regards,
Aki Niimura

[David Golightly]

On Aug 28, 6:40 pm, [e-mail] wrote:

I thought such scheme was already available, but so far, I don't see
anything usable.
The Web server is not a commercial one but a custom Web server
(written in Python) so that I want to keep the scheme as simple as
possible. I checked AJAX but I'm not sure I can use AJAX in my
application.

Once a page is loaded, you can't push stuff from the server to the
client. The client has to request it first. That's how TCP works.

What you can do, instead, is use JavaScript to poll your server at
regular intervals to check for updates. You would probably end up
using the XMLHttpRequest object (or its equivalent) to check for these
updates.

-David

[Thomas 'PointedEars' Lahn]

David Golightly wrote:

On Aug 28, 6:40 pm, [e-mail] wrote:

>I thought such scheme was already available, but so far, I don't see
anything usable.
The Web server is not a commercial one but a custom Web server
(written in Python) so that I want to keep the scheme as simple as
possible. I checked AJAX but I'm not sure I can use AJAX in my
application.

Once a page is loaded, you can't push stuff from the server to the
client. The client has to request it first. That's how TCP works.

TCP has nothing to do with that. You mean HTTP.

http://en.wikipedia.org/wiki/TCP
http://en.wikipedia.org/wiki/HTTP
PointedEars
--
realism: HTML 4.01 Strict
evangelism: XHTML 1.0 Strict
madness: XHTML 1.1 as application/xhtml+xml
-- Bjoern Hoehrmann

[Randy Webb]

Bart Van der Donck said the following on 8/29/2007 7:20 PM:

Thomas 'PointedEars' Lahn wrote:

>Bart Van der Donck wrote:

>>Thomas 'PointedEars' Lahn wrote:

<snip>

>>>>A javascript programme:
[ snip code ]
It is merely ECMAScript-3-conforming code, or such a script or program.
Then I suggest we rename this group to 'comp.lang.ECMAScript-3-
conforming-code'. [...]

I am not particularly inclined to support that.

Me neither. Come on. It was a joke.

I see Thomas has changed his mind.

<URL:
http://groups.google.com/group/comp.lang.javascript/browse_frm/thread/7f888edb61e6bffd/06bc2cbbb05cd9e7?lnk=st&q=do+not+say+ajax&rnum=2#0 6bc2cbbb05cd9e7>

Post #20.

--
Randy
Chance Favors The Prepared Mind
comp.lang.javascript FAQ - http://jibbering.com/faq/index.html
Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/

[akineko]

David Golightly wrote:

Thomas 'PointedEars' Lahn wrote:

Bart Van der Donck wrote:

Randy Webb wrote:

I would like to thank all of you guys to respond to my posting (more
than I hoped).
I really thank Bart for creating a test script and demonstrating that
it is feasible.

Probably this is not new for you guys here but what Bart has
demonstrated is un-tapped potentials.
Outside this group, actually I'm a hardware guy rather than a software
guy, not many people realizes such capabilities the browser can
unleash.

I will review the posting and I will incorporate the idea here to my
application.

Aki-

[Thomas 'PointedEars' Lahn]

Randy Webb wrote:

Bart Van der Donck said the following on 8/29/2007 7:20 PM:

>Thomas 'PointedEars' Lahn wrote:

>>Bart Van der Donck wrote:
Thomas 'PointedEars' Lahn wrote:
>A javascript programme:
>[ snip code ]
It is merely ECMAScript-3-conforming code, or such a script or program.
Then I suggest we rename this group to 'comp.lang.ECMAScript-3-
conforming-code'. [...]
I am not particularly inclined to support that.

Me neither. Come on. It was a joke.

I see Thomas has changed his mind.

<spockIs anything wrong with the one I have? </spock>

<URL:
http://groups.google.com/group/comp.lang.javascript/browse_frm/thread/7f888edb61e6bffd/06bc2cbbb05cd9e7?lnk=st&q=do+not+say+ajax&rnum=2#0 6bc2cbbb05cd9e7>

Post #20.

Not really. If you read what you snipped, I explain why I think it is a bad
idea to rename the newsgroup. The reasoning is the same (the group would
hardly be found even though the name would be better), the explanation this
time is just more verbose. You will also observe that the suggestion was
different this time (the previous one was more reasonable; and yes, I got
Bart's joke right away), hence a different reaction.

I also wonder why you find it necessary to state that you *think* you have
seen me change my mind. (If you follow my postings more closely, you will
observe that this happens often if I am presented with valid reasons to do so.)
HTH & HAND

PointedEars
--
"Use any version of Microsoft Frontpage to create your site. (This won't
prevent people from viewing your source, but no one will want to steal it.)"
-- from <http://www.vortex-webdesign.com/help/hidesource.htm>

[Bart Van der Donck]

Time for some conclusions in this thread.

- The use of a charset is not required by HTTP specifications, but it
is recommended.
- A javascript engine is a implementation of (a version of) an
ECMAScript specification.
- You were not able to proof any of your positions in a real-world
environment. You did perform a few interesting tests in the lab
though.
- Don't code, discuss or feature-detect Ex Absurdum.
- Using date() is recommended for randomizing URIs. Math.random() may
be used as well under "common sense" conditions.
- The original poster received a working, practical, cross-browser and
suitable answer to his question.
- There are more than sheer technical arguments, and they're often
more important.
- Use the right Content-Type.
- There is a difference between theory and practice.
- Type a smiley when telling a joke.

--
Bart

[Dr J R Stockton]

In comp.lang.javascript message <11**********************@d55g2000hsg.go
oglegroups.com>, Wed, 29 Aug 2007 12:13:37, Bart Van der Donck
<ba**@nijlen.composted:

> ajax('file.py?' + (new Date()).getTime(), '', '');

That is conceptually better, yes. But any idea about which scale we're
talking here ? Math.random() gives me 15 to 18 digits after comma,
let's say 16 for easy calculation.

In that case, it probably gives about 2^53 different values. However,
Opera 9.21 & 9.23 give only about 2^31 values, or so it seems.

In cases where each state of the PRNG gives a different value to
Math.random(), the latter will NOT repeat until all states have been
traversed.

--
(c) John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v6.05 IE 6.
Web <URL:http://www.merlyn.demon.co.uk/- FAQish topics, acronyms, & links.
I find MiniTrue useful for viewing/searching/altering files, at a DOS prompt;
free, DOS/Win/UNIX, <URL:http://www.idiotsdelight.net/minitrue/unsupported.

[Bart Van der Donck]

Dr J R Stockton wrote:

In comp.lang.javascript message <[e-mail]
oglegroups.com>, Wed, 29 Aug 2007 12:13:37, Bart Van der Donck
<[e-mail]:

>> ajax('file.py?' + (new Date()).getTime(), '', '');

>That is conceptually better, yes. But any idea about which scale we're
talking here ? Math.random() gives me 15 to 18 digits after comma,
let's say 16 for easy calculation.

In that case, it probably gives about 2^53 different values. However,
Opera 9.21 & 9.23 give only about 2^31 values, or so it seems.

In cases where each state of the PRNG gives a different value to
Math.random(), the latter will NOT repeat until all states have been
traversed.

I was not aware of that, and find it surprising. I sofar I remember my
math classes, a true randomizer should be like Thomas said, namely,
although a chance is statistically extremely unlikely, it can never be
excluded (cfr. "It's possible to win the lottery every week").

I think date() is conceptually better here.

--
Bart

[Bart Van der Donck]

The Natural Philosopher wrote:

Bart Van der Donck wrote:

>The academic world evaluates software using these criteria:
- maintainable
- adaptable
- transparent
- user-friendly
- reliable
- efficient

All software is a bloody compromise between all of those.
Now and again some academic writes a learned paper about how to achieve
one or other of them absolutely, but never mentions the disastrous
effect it has on some or all of the others.

I couldn't agree more.

--
Bart

[Dr J R Stockton]

In comp.lang.javascript message <11**********************@m37g2000prh.go
oglegroups.com>, Fri, 31 Aug 2007 01:16:40, Bart Van der Donck
<ba**@nijlen.composted:

>Dr J R Stockton wrote:

>In cases where each state of the PRNG gives a different value to
Math.random(), the latter will NOT repeat until all states have been
traversed.

I was not aware of that, and find it surprising.

It is an inevitable property of any digital pseudo-random number
generator in which the next output and the next internal state are
entirely determined by the internal state.

For those writing ECMA/ISO/IEC standard version 4 or 5 : it is a defect
of Javascript that the internal state of the PRNG is not read/write
accessible. If accessible, it would be possible for testing to generate
the same set of random numbers as often as desired.

<URL:http://www.merlyn.demon.co.uk/js-randm.htmshows the basics of a
reproducible PRNG method in Javascript, using a 32-bit seed and a known-
good constant. Conversion to 48-bit seed requires a good constant to be
found (Knuth?). Conversion to more than 52 or 53 bits would need real
work, but a good constant is available.

It's a good idea to update the newsgroup c.l.j and its FAQ. See below.

--
(c) John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v6.05 IE 6
news:comp.lang.javascript FAQ <URL:http://www.jibbering.com/faq/index.html>.
<URL:http://www.merlyn.demon.co.uk/js-index.htmjscr maths, dates, sources.
<URL:http://www.merlyn.demon.co.uk/TP/BP/Delphi/jscr/&c, FAQ items, links.