Hello comp.lang.js.I need a script to rotate a background image on
each newpage load, given the id of the element and a list (array?)of 2 or
more image paths ("img1.jpg", "img2.jpg", ...).Actually, depending on
how I write the HTML, I guess I'dneed the script to set
style.backgroun dImage or src.I'd need to run it on a few elements, something
like:setRandomB gImg('thingy1', ('img1a','img1b ', ...)
)setRandomBgImg ('thingy2', ('img2a','img2b ', ...) ) etcBut I don't actually know any more
javascript. :(Can you help? Thanks!! Lucy
6  2107 
This Little script let you cicle between 2 images
<body>
<script language = "Javascript ">
<!--
//nº of pictures
var npic=Math.round (Math.random())
//name of pictures
namepics= new Array("1.jpg"," 2.jpg");
document.write( "<img src='" + namepics[npic] + "' >");
//-->
</script>
</body>
Unfortunatelly I haven´t figure out out to work with more than two images
tough
Again here is a solution that works perfectly for 5 (five)
images
<script language="Javas cript">
<!--
npic=Math.rando m()
if (npic < 0.2)
document.write( "<img src=1.jpg>");
else if (npic <0.4)
document.write( "<img src=2.jpg>");
else if (npic <0.6)
document.write( "<img src=3.jpg>");
else if (npic <0.8)
document.write( "<img src=4.jpg>");
else
document.write( "<img src=5.jpg>");
//-->
</script>
On Fri, 24 Sep 2004 17:15:13 +0100, Oscar Monteiro <of**@hotmail.c om>
wrote: This Little script let you cicle between 2 images
<body>
<script language = "Javascript ">
The language attribute is deprecated in favour of the (required) type
attribute.
<script type="text/javascript">
<!--
There is no longer a need to hide scripts from old browsers. All user
agents currently in use understand the SCRIPT element.
//nº of pictures
var npic=Math.round (Math.random())
//name of pictures
namepics= new Array("1.jpg"," 2.jpg");
document.write( "<img src='" + namepics[npic] + "' >");
[snip]
Unfortunatelly I haven´t figure out out to work with more than two images
tough
How about
var pics = ['1.jpg', '2.jpg', '3.jpg', '4.jpg' /* etc... */];
document.write( '<img src="'
+ pics[Math.floor((Mat h.random() % 1) * pics.length)]
+ '" alt="">');
(Math.random() % 1) produces a real number in the range 0 <= n < 1. The
modulus ensures that buggy implementations don't return 1.0. Multiplying
by 'm' changes that range to 0 <= n < m. Using Math.ceil() then produces
an integer with a maximum value of (m - 1).
Of course, this doesn't actually change a background image. For this, use
the style object:
var b, s;
if((b = document.body) && (s = b.style)) {
var pics = ['1.jpg', '2.jpg', '3.jpg', '4.jpg' /* etc... */];
s.backgroundIma ge =
pics[Math.floor((Mat h.random() % 1) * pics.length)];
}
(untested)
Hope that helps,
Mike
--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.
JRS: In article <41************ **********@news .telepac.pt>, dated Fri,
24 Sep 2004 19:00:56, seen in news:comp.lang. javascript, Oscar Monteiro
<of**@hotmail.c om> posted : Again here is a solution that works perfectly for 5 (five)
images
<script language="Javas cript">
Deprecated<!--
npic=Math.rand om()
if (npic < 0.2)
document.write ("<img src=1.jpg>");
else if (npic <0.4)
document.write ("<img src=2.jpg>");
else if (npic <0.6)
document.write ("<img src=3.jpg>");
else if (npic <0.8)
document.write ("<img src=4.jpg>");
else
document.write ("<img src=5.jpg>");
//-->
</script>
But it would be much more elegant and extensible to use Random (FAQ
4.22) to generate the variable part of the array name :
document.write( "img src=", Random(5)+1, ".jpg>")
or to index an array of names
var Arr = ["this", "that", "tother"]
document.write( "img src=" + Arr[Random(Arr.leng th)] + ".jpg>")
In article <41************ **********@news .telepac.pt>, dated Fri, 24 Sep
2004 17:15:13, seen in news:comp.lang. javascript, Oscar Monteiro
<of**@hotmail.c om> posted :
var npic=Math.round (Math.random())
namepics= new Array("1.jpg"," 2.jpg");
document.write ("<img src='" + namepics[npic] + "' >");
Let that be a lesson to those who think that Math.round with Math.random
is always wrong !
--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://www.jibbering.c om/faq/> JL/RC: FAQ of news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> jscr maths, dates, sources.
<URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/jscr/&c, FAQ items, links.
Oscar Monteiro wrote: This Little script let you cicle between 2 images
<body>
<script language = "Javascript ">
<script type="text/javascript">
<!--
Don't, there is no standard for this. More, it is obsolete
and can only get you in more trouble if the script engine
does not support the non-standard approach.
//nº of pictures
var npic=Math.round (Math.random())
Math.random() returns a floating-point number between 0 and 1.
Math.round(...) rounds that number to the next integer number,
i.e. `npic' can assume only one of the values 0 or 1. This
is pertinent for a two-element array, but it certainly is not
for arrays with a different length.
//name of pictures
namepics= new Array("1.jpg"," 2.jpg");
Variables should be declared using the `var' keyword to avoid
side effects in functions (omitting the `var' keyword always
declares globals).
document.write( "<img src='" + namepics[npic] + "' >");
//-->
Don't, see above.
</script>
</body>
Unfortunatelly I haven´t figure out out to work with more than two images
^[1]
The reason is that your random number computation does not make any sense
with more than two elements in the array (indexes 0 and 1). Instead, you
should use the length of the array to compute an integer number in range:
var
namepics = new Array("1.jpg", "2. jpg", "3.jpg"),
npics = Math.round(Math .random() * namepics.length );
document.write( '<img src="' + namepics[npic] + '" alt="...">');
(Don't forget the "alt" attribute, it is required for Valid HTML! For
reasonable and barrier-free authoring the array should hold an Object
object providing at least both the image filename and the alternative
text, such as
var namepics = [
{src: "1.jpg", alt: "one"},
{src: "2.jpg", alt: "two"},
{src: "3.jpg", alt: "three"}
];
...
document.write(
"<img src='" + namepics[npic].src
+ "' alt="' + namepics[npic].alt + '">');
)
Your second solution in <news:41******* *************** @news.telepac.p t>
works indeed, however it is hard to maintain as with every new image you
have to re-compute the fraction which an element needs to match; yet,
*computing* is what *computers* were built for.
PointedEars
___________
[1] Please declare your character set and don't use accents as apostrophes,
see <http://insideoe.tomste rdam.com/>.
--
Vacuume Cleaner for computers: format C:
JRS: In article <13************ ****@PointedEar s.de>, dated Sun, 10 Oct
2004 15:16:05, seen in news:comp.lang. javascript, the infant Thomas
'PointedEars' Lahn <Po*********@we b.de> posted, in response to an
article over a fortnight old, in a thread that was completed long ago :
The reason is that your random number computation does not make any sense
with more than two elements in the array (indexes 0 and 1). Instead, you
should use the length of the array to compute an integer number in range:
var
namepics = new Array("1.jpg", "2. jpg", "3.jpg"),
npics = Math.round(Math .random() * namepics.length );
document.write( '<img src="' + namepics[npic] + '" alt="...">');
AIUI, the three elements of namepics are indexed 0, 1, 2;
namepics.length is 3, and npics will be assigned the values 0, 1, 2, 3
with probabilities about 17%, 33%, 33%, 17%.
Indexing namepics with npic gives an error message; with npics gives an
undefined element 16% of the time.
It is an elementary error; one that those who are familiar with
newsgroup FAQ item 4.22 should not be making. IMHO, "your random number
computation does not make any sense".
--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://www.jibbering.c om/faq/> JL/RC: FAQ of news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> jscr maths, dates, sources.
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