Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations strongm on being selected by the Tek-Tips community for having the most helpful posts in the forums last week. Way to Go!
Syntax question
- Thread starter vladibo
- Start date
- Thread starter
- #3
This guy is very good:
I am impressed but I don't understand everything.
I am impressed but I don't understand everything.
the double-! is pointless, all it does is double-negate, which is the same as having no !'s in the first place. see this example:
*cLFlaVA
----------------------------
[tt]mr. pibb + red vines = crazy delicious![/tt]
[URL unfurl="true"]http://www.coryarthus.com/[/url]
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"[URL unfurl="true"]http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">[/URL]
<html>
<head>
<title>Untitled</title>
</head>
<body>
<script type="text/javascript"><!--
document.write( true + "<br />");
document.write( !true + "<br />");
document.write( !!true + "<br />");
//--></script>
</body>
</html>*cLFlaVA
----------------------------
[tt]mr. pibb + red vines = crazy delicious![/tt]
[URL unfurl="true"]http://www.coryarthus.com/[/url]
The double negative is not totally vain, just a little device to make type cast to boolean more visible/explicit. (I am not disagreeing with cLFlaVA though.) The pont there is something line appending a "" to a scalar to make string operation less prong to unexpected error in case the undefined/null turn up.
[tt]s=null; s=""+s;[/tt]
The same here for double negation.
[tt]
function x
{
alert ("[y]\t"+y+"\t"+typeof+"\n"+"[!y]\t"+!y+"\t"+typeof(!y)+"\n"+"[!!y]\t"+!!y+"\t"+typeof(!!y))
}
x();
x("a");
x(true);
x(false);
x(1);
x(null);
x(new Array());
[/tt]
which make boolean type more certain.
Say for instance, a common occurrence of document.all for testing ie, we can make type casting more explicit and in a sense more comforting/ease of mind for the scripter by doing this.
[tt]if (!!document.all) {
// etc ...
}[/tt]
Just a little trick which might catch the eyes.
[tt]s=null; s=""+s;[/tt]
The same here for double negation.
[tt]
function x
{alert ("[y]\t"+y+"\t"+typeof
+"\n"+"[!y]\t"+!y+"\t"+typeof(!y)+"\n"+"[!!y]\t"+!!y+"\t"+typeof(!!y))}
x();
x("a");
x(true);
x(false);
x(1);
x(null);
x(new Array());
[/tt]
which make boolean type more certain.
Say for instance, a common occurrence of document.all for testing ie, we can make type casting more explicit and in a sense more comforting/ease of mind for the scripter by doing this.
[tt]if (!!document.all) {
// etc ...
}[/tt]
Just a little trick which might catch the eyes.
- Thread starter
- #6
- Status