using a minus in javascript

[mantrid]

I have the following link to bring up an alert with a figure in it based on
the screen resolution. but instead of displaying a number 'NaN' is
displayed.

<a href="javascrip t:alert('Your ideal estimated height is '+
screen.height*0 .55-screen.height*0 .2);" class="BodyLink ">Click to calculate
height </a>

But when I remove the part of the equation '-screen.height*0 .2' a figure is
displayed properly. Why doesnt it work when I have a minus in the equation.
Im not experienced with javascript so excuse if this is a basic question

thanks
ian

[mantrid]

any good links to doing calculations with javascript would also be very much
appreciated
"mantrid" <ia********@vir gin.netwrote in message
news:Wa******** *********@newsf e2-gui.ntli.net...

I have the following link to bring up an alert with a figure in it based

on

the screen resolution. but instead of displaying a number 'NaN' is
displayed.

<a href="javascrip t:alert('Your ideal estimated height is '+
screen.height*0 .55-screen.height*0 .2);" class="BodyLink ">Click to

calculate

height </a>

But when I remove the part of the equation '-screen.height*0 .2' a figure

is

displayed properly. Why doesnt it work when I have a minus in the

equation.

Im not experienced with javascript so excuse if this is a basic question

thanks
ian

[Lee]

mantrid said:

>
I have the following link to bring up an alert with a figure in it based on
the screen resolution. but instead of displaying a number 'NaN' is
displayed.

<a href="javascrip t:alert('Your ideal estimated height is '+
screen.height* 0.55-screen.height*0 .2);" class="BodyLink ">Click to calculate
height </a>

But when I remove the part of the equation '-screen.height*0 .2' a figure is
displayed properly. Why doesnt it work when I have a minus in the equation.
Im not experienced with javascript so excuse if this is a basic question

You're actually having trouble with the "+" operator, not the "-".
Your code:
1. calculates screen.height*0 .55
2. concatenates that value with "Your idea estimated height is ".
3. calculates screen.height*0 .2
4. tries to subtract that value from the string result of step 2
which is Not a Number.

Enclose your subtraction in parentheses, so it will be performed
before the concatenation:

'Your ideal estimated height is '+(screen.heigh t*0.55-screen.height*0 .2)

You really shouldn't be abusing he side-effect of the javascript:
pseudo-protocol that way, but if you must, you should have the
event handler return false to prevent the page from reloading
each time the link is clicked:

href="javascrip t:alert('Your ideal estimated height is '+
(screen.height* 0.55-screen.height*0 .2));return false"
--

[manxomfoe]

Your statement is being confused by something called operator
presidence. Try wrapping the math part of the equation in an extra set
of parens like this:

alert('Your ideal estimated height is ' + (screen.height * 0.55 -
screen.height * 0.2))
It forces the equation to evaluate a number before trying to convert it
to a string and attach it to your message. As you had it written, the
equation was doing the multiplication operators first, then adding the
"Your ideal...." string to the first number, making it a string. When
it tried to subtract the second number, the parser thought "I can't
subtract a number from a string" and threw NaN at you instead.

Cheers!

</bd>
mantrid wrote:

any good links to doing calculations with javascript would also be very much
appreciated
"mantrid" <ia********@vir gin.netwrote in message
news:Wa******** *********@newsf e2-gui.ntli.net...

I have the following link to bring up an alert with a figure in it based

on

the screen resolution. but instead of displaying a number 'NaN' is
displayed.

<a href="javascrip t:alert('Your ideal estimated height is '+
screen.height*0 .55-screen.height*0 .2);" class="BodyLink ">Click to

calculate

height </a>

But when I remove the part of the equation '-screen.height*0 .2' a figure

is

displayed properly. Why doesnt it work when I have a minus in the

equation.

Im not experienced with javascript so excuse if this is a basic question

thanks
ian

[mantrid]

Thanks

You really shouldn't be abusing he side-effect of the javascript:
pseudo-protocol that way, but if you must, you should have the
event handler return false to prevent the page from reloading
each time the link is clicked:

excuse my ignorance but can you clarify this. why is it abuse?

[mantrid]

thanks
that worked

"manxomfoe" <br**********@g mail.comwrote in message
news:11******** **************@ j72g2000cwa.goo glegroups.com.. .

Your statement is being confused by something called operator
presidence. Try wrapping the math part of the equation in an extra set
of parens like this:

alert('Your ideal estimated height is ' + (screen.height * 0.55 -
screen.height * 0.2))
It forces the equation to evaluate a number before trying to convert it
to a string and attach it to your message. As you had it written, the
equation was doing the multiplication operators first, then adding the
"Your ideal...." string to the first number, making it a string. When
it tried to subtract the second number, the parser thought "I can't
subtract a number from a string" and threw NaN at you instead.

Cheers!

</bd>
mantrid wrote:

any good links to doing calculations with javascript would also be very

much

appreciated
"mantrid" <ia********@vir gin.netwrote in message
news:Wa******** *********@newsf e2-gui.ntli.net...

I have the following link to bring up an alert with a figure in it

based

on

the screen resolution. but instead of displaying a number 'NaN' is
displayed.
>
<a href="javascrip t:alert('Your ideal estimated height is '+
screen.height*0 .55-screen.height*0 .2);" class="BodyLink ">Click to

calculate

height </a>
>
But when I remove the part of the equation '-screen.height*0 .2' a

figure

is

displayed properly. Why doesnt it work when I have a minus in the

equation.

Im not experienced with javascript so excuse if this is a basic

question

>
thanks
ian
>
>
>

[mick white]

mantrid wrote:

any good links to doing calculations with javascript would also be very much
appreciated
"mantrid" <ia********@vir gin.netwrote in message
news:Wa******** *********@newsf e2-gui.ntli.net...

>>I have the following link to bring up an alert with a figure in it based

on

>>the screen resolution. but instead of displaying a number 'NaN' is
displayed.

<a href="javascrip t:alert('Your ideal estimated height is '+
screen.height *0.55-screen.height*0 .2);" class="BodyLink ">Click to

calculate

>>height </a>

Why not:
alert('Your ideal estimated height is '+screen.height *0.53)
?
screen.height*0 .55-screen.height*0 .2==screen.heig ht*0.53, no?
Mick

>>
But when I remove the part of the equation '-screen.height*0 .2' a figure

is

>>displayed properly. Why doesnt it work when I have a minus in the

equation.

>>Im not experienced with javascript so excuse if this is a basic question

thanks
ian

[Lee]

mantrid said:

>
Thanks

>You really shouldn't be abusing he side-effect of the javascript:
pseudo-protocol that way, but if you must, you should have the
event handler return false to prevent the page from reloading
each time the link is clicked:

excuse my ignorance but can you clarify this. why is it abuse?

First I need to point out that my advice to add "return false"
was incorrect. I was thinking of something else when I wrote
that. I'm getting old.

The intention of the javascript: pseudo-protocol is that the
Javascript expression will be evaluated and the resulting HTML
will replace the current contents of the page. What you're
doing is exploiting the side-effect. Your code doesn't return
any HTML, so the current contents are not replaced.

It's abuse because the browser is still expecting to load the
returned contents as a new page. This means that if you make
a little mistake that causes a value to be returned, you're
going to be back here asking why clicking this link replaces
your page with one that contains nothing but the string
"[Object]", or "[Window]", etc, and because certain other
operations cause unpredictable results in some browsers when
the browser thinks that it's about to load new content.
it's about to
--

[Evertjan.]

manxomfoe wrote on 03 dec 2006 in comp.lang.javas cript:

Your statement is being confused by something called operator
presidence.

Indeed, but it should be "operator precedence".
--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Bart Lateur]

manxomfoe wrote:

>Your statement is being confused by something called operator
presidence.

It's "precedence ".

--
Bart.