Whats wrong with this?

[TheShadow1]

<script type="text/JavaScript" src="here.js">
<!--
function output() {
var i = Math.round(5*Ma th.random());
document.write( safetyTips[i]);
}
output();
//-->
</script>

safetyTips[] - this array is in here.js ...

[Evertjan.]

TheShadow1 wrote on 02 apr 2005 in comp.lang.javas cript:

<script type="text/JavaScript" src="here.js">
<!--
function output() {
var i = Math.round(5*Ma th.random());
document.write( safetyTips[i]);
}
output();
//-->
</script>

You cannot have both an external and inline scripting
with the same <script> block.

Don't use <!--, //-->, outdated for years.

--
Evertjan.
The Netherlands.
(Replace all crosses with dots in my emailaddress)

[RobG]

TheShadow1 wrote:

<script type="text/JavaScript" src="here.js">
<!--
function output() {
var i = Math.round(5*Ma th.random());
document.write( safetyTips[i]);
}
output();
//-->
</script>

safetyTips[] - this array is in here.js ...

Evertjan has already fixed your main problem, but you also have given
yourself a maintenance problem by hard-coding (I presume) the length
of your array.

Given the general nature of the question in your subject, I'll add
that you can also make it more concise (I've used 'sT' for the name
of the safteyTips array to avoid wrapping):

<script type="text/javascript" src="here.js"></script>
<script type="text/javascript">
document.write( sT[Math.round((sT. length-1)*Math.random( ))]);
</script>

is all that is required.

--
Rob

[Lee]

RobG said:

TheShadow1 wrote:

<script type="text/JavaScript" src="here.js">
<!--
function output() {
var i = Math.round(5*Ma th.random());
document.write( safetyTips[i]);
}
output();
//-->
</script>

safetyTips[] - this array is in here.js ...

Evertjan has already fixed your main problem, but you also have given
yourself a maintenance problem by hard-coding (I presume) the length
of your array.

Given the general nature of the question in your subject, I'll add
that you can also make it more concise (I've used 'sT' for the name
of the safteyTips array to avoid wrapping):

<script type="text/javascript" src="here.js"></script>
<script type="text/javascript">
document.write( sT[Math.round((sT. length-1)*Math.random( ))]);

Using Math.round() underselects the first and last elements of the array.
sT[Math.floor(Math .random()*sT.le ngth)]

[Lasse Reichstein Nielsen]

RobG <rg***@iinet.ne t.auau> writes:

document.write( sT[Math.round((sT. length-1)*Math.random( ))]); .... is all that is required.

Don't use Math.round like this, it gives the first and last element
only half the chance of the others.

Use:

sT[Math.floor(Math .random() * sT.length)]
/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

[Mick White]

Lasse Reichstein Nielsen wrote:

RobG <rg***@iinet.ne t.auau> writes:

document.write( sT[Math.round((sT. length-1)*Math.random( ))]);

...

is all that is required.

Don't use Math.round like this, it gives the first and last element
only half the chance of the others.

Use:

sT[Math.floor(Math .random() * sT.length)]

or:
sT[new Date()%sT.lengt h]

Mick

[RobG]

Lee wrote:

RobG said:

[...]

<script type="text/javascript" src="here.js"></script>
<script type="text/javascript">
document.write( sT[Math.round((sT. length-1)*Math.random( ))]);

Using Math.round() underselects the first and last elements of the array.
sT[Math.floor(Math .random()*sT.le ngth)]

I was going to comment on the possibility that the selection was not
even for all elements in the array, however using Math.floor as
suggested infers that Math.random will *never* return 1, or at least
that the index will never be evaluated to be the length of the array.

Should that occur, the tip of the day will be 'undefined'.

The specification says that Math.random will return a value "greater
than or equal to 0 but less than 1" which means that in theory the
.floor method is OK, but is it in practice?
--
Rob

[Richard Cornford]

RobG wrote:

Lee wrote:

<snip>

Using Math.round() underselects the first and last elements of the
array. sT[Math.floor(Math .random()*sT.le ngth)]

I was going to comment on the possibility that the selection was not
even for all elements in the array, however using Math.floor as
suggested infers that Math.random will *never* return 1, or at least
that the index will never be evaluated to be the length of the
array.

Should that occur, the tip of the day will be 'undefined'.

The specification says that Math.random will return a value "greater
than or equal to 0 but less than 1" which means that in theory the
.floor method is OK, but is it in practice?

Apparently a now every old Opera version (I think it was 4 but it may
have been 5) had a buggy Math.random that did occasionally return 1. I
have not heard mention of any other javascript versions with the same
problem. Absolute safety can be guaranteed with - Math.random() % 1 -.

A faster alternative to Math.floor in this context could be an OR zero
operation:-

array.sT[((Math.random() *sT.length) | 0)]

As OR zero truncates numbers with fractional parts into integers. It
also restricts the possible range of those integers to 32 bit signed
integers, which is half of the specified possible range for Array
indexes (though that should not be a problem in most cases).

Richard.

[Dr John Stockton]

JRS: In article <nG************ ****@twister.ny roc.rr.com>, dated Sat, 2
Apr 2005 19:48:35, seen in news:comp.lang. javascript, Mick White
<mw***********@ rochester.rr.co m> posted :

Lasse Reichstein Nielsen wrote:

RobG <rg***@iinet.ne t.auau> writes:

document.write( sT[Math.round((sT. length-1)*Math.random( ))]);

...

is all that is required.

Don't use Math.round like this, it gives the first and last element
only half the chance of the others.

Use:

sT[Math.floor(Math .random() * sT.length)]

or:
sT[new Date()%sT.lengt h]

I think that the OP has a 5-element array.
Have you tried your method with 5 or 10 elements in the array?
Actually, AFAIK, it *might* work in XP, and *might* in non-PC; but I
don't expect it to in NT, and it does not in Win98.

Do any systems show a 1 ms resolution for X = new Date() ?

<FAQENTRY> :

I find that
(Math.random()* 10)|0
is appreciably faster than
Math.floor(Math .random()*10)
although the latter might be considered more readable.

If tests on other systems show similar results, ISTM that it would be
worth adding the former to FAQ 4.22, and taking the opportunity to
remark that |0 can beat Math.floor.

--
© 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.

[Mick White]

Dr John Stockton wrote:

JRS: In article <nG************ ****@twister.ny roc.rr.com>, dated Sat, 2
Apr 2005 19:48:35, seen in news:comp.lang. javascript, Mick White
<mw***********@ rochester.rr.co m> posted :

Lasse Reichstein Nielsen wrote:

RobG <rg***@iinet.ne t.auau> writes:

document.write( sT[Math.round((sT. length-1)*Math.random( ))]);

...
is all that is required.
Don't use Math.round like this, it gives the first and last element
only half the chance of the others.

Use:

sT[Math.floor(Math .random() * sT.length)]
or:
sT[new Date()%sT.lengt h]

I think that the OP has a 5-element array.
Have you tried your method with 5 or 10 elements in the array?
Actually, AFAIK, it *might* work in XP, and *might* in non-PC; but I
don't expect it to in NT, and it does not in Win98.

Well, John, new Date() is cast as a Number in a Modulus operation.

sT[new Date().getTime( )%sT.length] will force the conversion though, and
create equal distribution of the array entries. Since the datestamp is a
large dynamic number, its use is ideal in this scenario (one off).
I don't know why it wouldn't work in NT or Win98, please educate me.
Mick

Do any systems show a 1 ms resolution for X = new Date() ?
<FAQENTRY> :

I find that
(Math.random()* 10)|0
is appreciably faster than
Math.floor(Math .random()*10)
although the latter might be considered more readable.

If tests on other systems show similar results, ISTM that it would be
worth adding the former to FAQ 4.22, and taking the opportunity to
remark that |0 can beat Math.floor.