urn page 2 - Dave's Blog

The DOM location interface exposes the HTML document's URI parsed into its properties. However, it is ancient and has problems that bug me but otherwise rarely show up in the real world. Complaining about mostly theoretical issues is why blogging exists, so here goes:

• The location object's search, hash, and protocol properties are all misnomers that lead to confusion about the correct terms:
  • The 'search' property returns the URI's query property. The query property isn't limited to containing search terms.
  • The 'hash' property returns the URI's fragment property. This one is just named after its delimiter. It should be called the fragment.
  • The 'protocol' property returns the URI's scheme property. A URI's scheme isn't necessarily a protocol. The http URI scheme of course uses the HTTP protocol, but the https URI scheme is the HTTP protocol over SSL/TLS - there is no HTTPS protocol. Similarly for something like mailto - there is no mailto wire protocol.
• The 'hash' and 'search' location properties both return null in the case that their corresponding URI property doesn't exist or if its the empty string. A URI with no query property and a URI with an empty string query property that are otherwise the same, are not equal URIs and are allowed by HTTP to return different content. Similarly for the fragment. Unless the specific URI scheme defines otherwise, an empty query or hash isn't the same as no query or hash.

But like complaining about the number of minutes in an hour none of this can ever change without huge compat issues on the web. Accordingly I can only give my thanks to Anne van Kesteren and the awesome work on the URL standard moving towards a more sane (but still working practically within the constraints of compat) location object and URI parsing in the browser.

PowerShell nicely includes ConvertTo-CSV and ConvertFrom-CSV which allow you to serialize and deserialize your PowerShell objects to and from CSV. Unfortunately the CSV produced by ConvertTo-CSV is not easily opened by Excel which expects by default different sets of delimiters and such. Looking online you'll find folks who recommend using automation via COM to create a new Excel instance and copy over the data in that fashion. This turns out to be very slow and impractical if you have large sets of data. However you can use automation to open CSV files with not the default set of delimiters. So the following isn't the best but it gets Excel to open a CSV file produced via ConvertTo-CSV and is faster than the other options:

Param([Parameter(Mandatory=$true)][string]$Path);

$excel = New-Object -ComObject Excel.Application

$xlWindows=2
$xlDelimited=1 # 1 = delimited, 2 = fixed width
$xlTextQualifierDoubleQuote=1 # 1= doublt quote, -4142 = no delim, 2 = single quote
$consequitiveDelim = $False;
$tabDelim = $False;
$semicolonDelim = $False;
$commaDelim = $True;
$StartRow=1
$Semicolon=$True

$excel.visible=$true
$excel.workbooks.OpenText($Path,$xlWindows,$StartRow,$xlDelimited,$xlTextQualifierDoubleQuote,$consequitiveDelim,$tabDelim,$semicolonDelim, $commaDelim);

See Workbooks.OpenText documentation for more information.

Occasionally I have need to run a set of unrelated promises in series, for instance an object dealing with a WinRT camera API that can only execute one async operation at a time, or an object handling postMessage message events and must resolve associated async operations in the same order it received the requests. The solution is very simply to keep track of the last promise and when adding a new promise in serial add a continuation of the last promise to execute the new promise and point the last promise at the result. I encapsulate the simple solution in a simple constructor:

    function PromiseExecutionSerializer() {
        var lastPromise = WinJS.Promise.wrap(); // Start with an empty fulfilled promise.

        this.addPromiseForSerializedExecution = function(promiseFunction) {
            lastPromise = lastPromise.then(function () {
                // Don't call directly so next promise doesn't get previous result parameter.
                return promiseFunction();
            });
        }
    }

The only thing to watch out for is to ensure you don't pass the result of a previous promise onto a subsequent promise that is unrelated.

When writing a JavaScript library that uses postMessage and the message event, I must be considerate of other JS code that will be running along side my library. I shouldn't assume I'm the only sender and receiver on a caller provided MessagePort object. This means obviously I should use addEventListener("message" rather than the onmessage property (see related What if two programs did this?). But considering the actual messages traveling over the message channel I have the issue of accidentally processing another libraries messages and having another library accidentally process my own message. I have a few options for playing nice in this regard:

Require a caller provided unique MessagePort

This solves the problem but puts a lot of work on the caller who may not notice nor follow this requirement.

Uniquely mark my messages

To ensure I'm acting upon my own messages and not messages that happen to have similar properties as my own, I place a 'type' property on my postMessage data with a value of a URN unique to me and my JS library. Usually because its easy I use a UUID URN. There's no way someone will coincidentally produce this same URN. With this I can be sure I'm not processing someone else's messages. Of course there's no way to modify my postMessage data to prevent another library from accidentally processing my messages as their own. I can only hope they take similar steps as this and see that my messages are not their own.

Use caller provided MessagePort only to upgrade to new unique MessagePort

I can also make my own unique MessagePort for which only my library will have the end points. This does still require the caller to provide an initial message channel over which I can communicate my new unique MessagePort which means I still have the problems above. However it clearly reduces the surface area of the problem since I only need once message to communicate the new MessagePort.

The best solution is likely all of the above.
Photo is Sharing by leezie5. Two squirrels sharing food hanging from a bird feeder. Used under Creative Commons license Attribution-NonCommercial-NoDerivs 2.0 Generic.

My first app for Windows 8 was Shout Text. You type into Shout Text, and your text is scaled up as large as possible while still fitting on the screen, as you type. It is the closest thing to a Hello World app as you'll find on the Windows Store that doesn't contain that phrase (by default) and I approached it as the simplest app I could make to learn about Windows modern app development and Windows Store app submission.

I rely on WinJS's default layout to use CSS transforms to scale up the user's text as they type. And they are typing into a simple content editable div.

The app was too simple for me to even consider using ads or charging for it which I learned more about in future apps.

The first interesting issue I ran into was that copying from and then pasting into the content editable div resulted in duplicates of the containing div with copied CSS appearing recursively inside of the content editable div. To fix this I had to catch the paste operation and remove the HTML data from the clipboard to ensure only the plain text data is pasted:

        function onPaste() {
            var text;

            if (window.clipboardData) {
                text = window.clipboardData.getData("Text").toString();
                window.clipboardData.clearData("Html");
                window.clipboardData.setData("Text", util.normalizeContentEditableText(text));
            }
        }
        shoutText.addEventListener("beforepaste", function () { return false; }, false);
        shoutText.addEventListener("paste", onPaste, false);

I additionally found an issue in IE in which applying a CSS transform to a content editable div that has focus doesn't move the screen position of the user input caret - the text is scaled up or down but the caret remains the same size and in the same place on the screen. To fix this I made the following hack to reapply the current cursor position and text selection which resets the screen position of the user input caret.

        function resetCaret() {
            setTimeout(function () {
                var cursorPos = document.selection.createRange().duplicate();
                cursorPos.select();
            }, 200);
        }

        shoutText.attachEvent("onresize", function () { resetCaret(); }, true);

The recent short story Twitter API returning results that do not respect arrow of time by Tim May written as a Twitter bug report reminded me of a few other short sci-fi stories written in the style of some sort of Internet document:

• comp.basalisk FAQ by David Langford written as a FAQ.
• Wikihistory by Desmond Warzel presented as a forum thread.
• The Riddle of the Universe and Its Solution by Christopher Cherian written as a scientific report.