We've all been there before - concatenating strings of html, but which way is quicker?
1) Recursive concatenation.
var html = "<html>" + "<head>" + "<title>";
2) Append to the variable.
var html = "<html>";
html += "<head>";
html += "<title>";
3) Join the array
var html = ["<html>", "<head>", "<title>"].join("");
Smart engines such as SpiderMonkey (the basis for Netscape's original JavaScript engine - leading to Netscape, Firefox, etc) would use exactly the same underlying code for examples 1 and 2 - no speed difference at all. JScript in example 2 however would look up the html variable each time and use an intermediary to store the new values before discarding the old ones. So there would be a speed differential in JScript where example 1 is quicker than example 2.
The fastest string concatenation is using option 3 - this is down to the array's internal string builder facility which allows for much faster string manipulation. Of course it's only going to make a big difference when contactenating strings over many iterations - such as creating a large html table. Over a very small number of iterations the difference is so negligable as to be inconsequential.
Showing posts with label jscript. Show all posts
Showing posts with label jscript. Show all posts
Tuesday, 12 December 2006
Tuesday, 21 November 2006
CSS image flickering solved in IE
There has been a problem for many years that most of us have come across developing for Internet Explorer with background images "flickering" when the cursor is hovering over them. (here's an example). This is due to to Internet Explorer checking for a new version of the background image declared in the background-image css attribute when the mouse hovers over the tag. The flicker issue may also be accompanied with the hourglass flicking on or even no image flicker, but the hourglass flickers!
<script type="text/javascript" language="javascript">
/*@cc_on @*/
/*@if (@_jscript_version >= 4)
document.execCommand("BackgroundImageCache", false, true);
/*@end @*/
</script>
Essentially, if you include this script somewhere in your page (best towards the top) then it will resolve this problem. Banzai!
The comments with all the @ symbols are actually JScript (Microsoft's version of JavaScript) conditional commenting. In simple terms, only IE will see and execute this code. In more complex terms it means only the IE compiler will read and compile this code. This means that should you have large forks in your script - one to deal with IE and another to deal with any other browsers - you can often get large performance returns from using conditional compiling. There's a good article on javascriptkit.com about conditional compilation of JScript.
I can't take credit for this solution - MisterPixel came up with the goods looking into DHTML behaviours in IE with regards to another problem (a bit like Fleming discovering penicillin!).
<script type="text/javascript" language="javascript">
/*@cc_on @*/
/*@if (@_jscript_version >= 4)
document.execCommand("BackgroundImageCache", false, true);
/*@end @*/
</script>
Essentially, if you include this script somewhere in your page (best towards the top) then it will resolve this problem. Banzai!
The comments with all the @ symbols are actually JScript (Microsoft's version of JavaScript) conditional commenting. In simple terms, only IE will see and execute this code. In more complex terms it means only the IE compiler will read and compile this code. This means that should you have large forks in your script - one to deal with IE and another to deal with any other browsers - you can often get large performance returns from using conditional compiling. There's a good article on javascriptkit.com about conditional compilation of JScript.
I can't take credit for this solution - MisterPixel came up with the goods looking into DHTML behaviours in IE with regards to another problem (a bit like Fleming discovering penicillin!).
Thursday, 16 November 2006
Registry hacking
Note: This is Internet Explorer only as it deals with ActiveX and modifying the system registry.
Recently I've been writing a few scripts to change values in the system registry. In actual fact, you use a few different technologies to achieve something that looks very simple. This script reads then sets the home page for Internet Explorer via the registry. However you can edit any registry value you wish to using this method.
Background
Firstly what is the registry? In simple terms, the registry is a database that stores settings and options for Windows and contains information for all the hardware, software and preferences of the PC (http://en.wikipedia.org/wiki/Regedit). This script uses a combination of JScript and ActiveX in a Windows Script host environment to edit those bits of information in the registry. JScript is Microsoft's Active Scripting implementation of ECMAScript (http://en.wikipedia.org/wiki/Jscript). Basically it's their version of JavaScript, but with lots of add-on features. These "add-ons" also rather nattily work in any Windows Script Host environment - and that's been shipped by default with every version of Windows since Windows 98 or with Internet Explorer 5+. Further information: http://en.wikipedia.org/wiki/Windows_Script_Host. We can use this JScript to create an ActiveX control to pass information from our script into the registry. ActiveX is simply as mechanism for passing information around a Windows computer. All in all, pretty neat eh?
Here's my script:
<script type="text/jscript" language="jscript">
var objShell = new ActiveXObject("WScript.shell");
/* Get the current home page */
var strRegKey = "HKCU\\Software\\Microsoft\\Internet Explorer\\Main\\Start Page";
var strCurrentHomepage = objShell.RegRead(strRegKey);
/* Set a new homepage */
objShell.RegWrite(strRegKey, "http://nargster.blogspot.com/");
</script>
Let's go through it.
The script attributes
<script type="text/jscript" language="jscript">
These are set to jscript because this script is only to work in IE it's not vital, but it's good a good habit to get into.
Create an Windows Script Host (WScript) shell object
var objShell = new ActiveXObject("WScript.shell");
OK, so we're going to ask the script to create a new ActiveX object (as mentioned, this is just an information carrier) to pass information to a particular target - in this case the Windows Script Host (WScript) shell. The shell is simply interface that enables access to the inner workings of the computer - we need to create this shell object in our script to access the registry.
Accessing the registry
var strRegKey = "HKCU\\Software\\Microsoft\\Internet Explorer\\Main\\Start Page";
var strCurrentHomepage = objShell.RegRead(strRegKey);
objShell.RegWrite(strRegKey, "http://nargster.blogspot.com/");
Now we've created a shell object, we can access the properties and methods of that object. Two of its methods are called RegRead and RegWrite - they read and write the registry respectively. The example shows the arguments required for these two methods. In both we pass the registry path of the registry item we wish to edit, making sure that we replace any single backslashes \ with a double backslash \\. This is because the backslash character in JScript is special - it's an escape character. The strRegKey string is the path to the value we want to change, you can find more information about how this string is built by looking through the registry using regedit, explained below. It's easy to see how the string relates to the structure of the registry, it's like a filesystem folder path.
Regedit - the registry editor
So you want to find out what the registry looks like to browse through. I'll not kid you - it's massive. You can use regedit, the registry editor (Start Menu --> Run, then type regedit and hit enter or run regedit.exe or regedt32.exe in your Windows directory) to have a look around and adventure. The registry structure is too detailed to go into here, but Wikipedia do an excellent job of it: http://en.wikipedia.org/wiki/Regedit
A last word just on security
It does seem incredible that Microsoft would create a web browser that could run scripting to read and write the system registry, but that's what they've done. They've tried to correct this problem in IE7 by not allowing the creation of ActiveX controls by default - users must enable this manually (with accompanying nasty messages about potential insecurities). In other supported versions of IE (IE3 - IE6) the default behaviour is that this simply runs with an ActiveX warning message. You can get around these warnings by saving the html file with an hta extension, turning the html file into an HTML application (MSDN). This .hta file only runs locally on a machine and runs without the strict security model the browser uses - no nasty error messages!
Play around with the registry - you could potentially damage something, but stick to the simple stuff and work your way up and it should all be good. Using .hta files is good because it opens all sorts of potential for html/scripting without security restrictions, so you can make cross-domain AJAX calls - something which is not allowed in a webpage) as well as other funky HTML applications to change the settings and tailor your computer.
Windows Script Host programming reference
There's loads of methods and properties of the shell object - you're not limited to reading and writing stuff to the registry - you can set/retrieve/delete user information, network and printer settings, read and write files and much more. You can find details of this at devguru.com in their Windows Script Host reference:
http://www.devguru.com/Technologies/wsh/quickref/wsh_intro.html
Recently I've been writing a few scripts to change values in the system registry. In actual fact, you use a few different technologies to achieve something that looks very simple. This script reads then sets the home page for Internet Explorer via the registry. However you can edit any registry value you wish to using this method.
Background
Firstly what is the registry? In simple terms, the registry is a database that stores settings and options for Windows and contains information for all the hardware, software and preferences of the PC (http://en.wikipedia.org/wiki/Regedit). This script uses a combination of JScript and ActiveX in a Windows Script host environment to edit those bits of information in the registry. JScript is Microsoft's Active Scripting implementation of ECMAScript (http://en.wikipedia.org/wiki/Jscript). Basically it's their version of JavaScript, but with lots of add-on features. These "add-ons" also rather nattily work in any Windows Script Host environment - and that's been shipped by default with every version of Windows since Windows 98 or with Internet Explorer 5+. Further information: http://en.wikipedia.org/wiki/Windows_Script_Host. We can use this JScript to create an ActiveX control to pass information from our script into the registry. ActiveX is simply as mechanism for passing information around a Windows computer. All in all, pretty neat eh?
Here's my script:
<script type="text/jscript" language="jscript">
var objShell = new ActiveXObject("WScript.shell");
/* Get the current home page */
var strRegKey = "HKCU\\Software\\Microsoft\\Internet Explorer\\Main\\Start Page";
var strCurrentHomepage = objShell.RegRead(strRegKey);
/* Set a new homepage */
objShell.RegWrite(strRegKey, "http://nargster.blogspot.com/");
</script>
Let's go through it.
The script attributes
<script type="text/jscript" language="jscript">
These are set to jscript because this script is only to work in IE it's not vital, but it's good a good habit to get into.
Create an Windows Script Host (WScript) shell object
var objShell = new ActiveXObject("WScript.shell");
OK, so we're going to ask the script to create a new ActiveX object (as mentioned, this is just an information carrier) to pass information to a particular target - in this case the Windows Script Host (WScript) shell. The shell is simply interface that enables access to the inner workings of the computer - we need to create this shell object in our script to access the registry.
Accessing the registry
var strRegKey = "HKCU\\Software\\Microsoft\\Internet Explorer\\Main\\Start Page";
var strCurrentHomepage = objShell.RegRead(strRegKey);
objShell.RegWrite(strRegKey, "http://nargster.blogspot.com/");
Now we've created a shell object, we can access the properties and methods of that object. Two of its methods are called RegRead and RegWrite - they read and write the registry respectively. The example shows the arguments required for these two methods. In both we pass the registry path of the registry item we wish to edit, making sure that we replace any single backslashes \ with a double backslash \\. This is because the backslash character in JScript is special - it's an escape character. The strRegKey string is the path to the value we want to change, you can find more information about how this string is built by looking through the registry using regedit, explained below. It's easy to see how the string relates to the structure of the registry, it's like a filesystem folder path.
Regedit - the registry editor
So you want to find out what the registry looks like to browse through. I'll not kid you - it's massive. You can use regedit, the registry editor (Start Menu --> Run, then type regedit and hit enter or run regedit.exe or regedt32.exe in your Windows directory) to have a look around and adventure. The registry structure is too detailed to go into here, but Wikipedia do an excellent job of it: http://en.wikipedia.org/wiki/Regedit
A last word just on security
It does seem incredible that Microsoft would create a web browser that could run scripting to read and write the system registry, but that's what they've done. They've tried to correct this problem in IE7 by not allowing the creation of ActiveX controls by default - users must enable this manually (with accompanying nasty messages about potential insecurities). In other supported versions of IE (IE3 - IE6) the default behaviour is that this simply runs with an ActiveX warning message. You can get around these warnings by saving the html file with an hta extension, turning the html file into an HTML application (MSDN). This .hta file only runs locally on a machine and runs without the strict security model the browser uses - no nasty error messages!
Play around with the registry - you could potentially damage something, but stick to the simple stuff and work your way up and it should all be good. Using .hta files is good because it opens all sorts of potential for html/scripting without security restrictions, so you can make cross-domain AJAX calls - something which is not allowed in a webpage) as well as other funky HTML applications to change the settings and tailor your computer.
Windows Script Host programming reference
There's loads of methods and properties of the shell object - you're not limited to reading and writing stuff to the registry - you can set/retrieve/delete user information, network and printer settings, read and write files and much more. You can find details of this at devguru.com in their Windows Script Host reference:
http://www.devguru.com/Technologies/wsh/quickref/wsh_intro.html
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