To llustrate the problem, type the following in the firebug console
and run it:
x = "100"
y = "200"
x += 1*y
console.log("x = "+x);
x = "100"
y = "200"
x = x + 1*y
console.log("x expanded = "+x);
You will see the string concatenation and result:
x= "100200"
x expanded = "100200"
The JS core documentation says that the addition + operator has a left-
to-right association and it also has a lower precedence over the
multiplication.
So 1*y should evaluated first to produce a numeric value, so we have:
string = string + postive_number*string
which becomes:
string = string + number
That would be a string concatenation as shown in the console above.
However using the unary negation resolve this:
x = "100"
y = "200"
x -= -1*y
console.log("x = "+x);
and you get x = 300.
Understanding this, this is how it expands:
x = x - -1*y
or
string = string - negative_number * string
which reduces to
string = string - number
so I guess, there is no bug here because this is not expected to
concatenate the parts here. A negative operator natually has the
presumption of arithmetic.
No bug!
Just one of those odd things one needs to keep in mind when using the
assigment += operator.
Never mind!
--
HLS
On Aug 23, 9:39 am, Pops <[EMAIL PROTECTED]> wrote:
> I posted this as a subtopic in another message,
>
> http://groups.google.com/group/jquery-en/browse_thread/thread/f54857c...
>
> but I now see that probably is a separate JS issue that the purist
> here might appreciate.
>
> Not to long ago, I came across JS behavior and just noted it down.
> The issue in the reference link above reminded me of this.
>
> This code is basically part of First, Prev, Next, Last, table
> navigator for our ad hoc report/table generator. It is pre-jQuery
> work. So here I am using the $() function to get the element.
>
> function $(v) { return(document.getElementById(v)); }
> function gotoPrevPage()
> {
> $("start").value -= 1*$("rows").value; // <- WORKS AS EXPECTED
>
> }
>
> function gotoNextPageBUG()
> {
> $("start").value += 1*$("rows").value; // <- BUG!!
>
> }
>
> function gotoNextPageFIX()
> {
> $("start").value -= -1*$("rows").value; // <- FIX!!
>
> }
>
> I was multiplying by 1 to help JS type cast the operation to tell it
> that it adding or substracting a number rather than a string. If you
> remove the multiplier, JS will naturally concatentate strings.
>
> But that didn't work for the gotoNextPage() function using the
> inclusive += operation. It worked fine with -= operation in
> gotoPrevPage().
>
> So I used the reverse logic to multiply by -1 instead with -= and it
> worked.
>
> To me, that looks look like a JS type casting bug or inclusive
> addition bug?
>
> What say you?
>
> --
> HLS
