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Data breakpoints in JavaScript

2016 Jun 17, 5:44

The other day I had to debug a JavaScript UWA that was failing when trying to use an undefined property. In a previous OS build this code would run and the property was defined. I wanted something similar to windbg/cdb's ba command that lets me set a breakpoint on read or writes to a memory location so I could see what was creating the object in the previous OS build and what that code was doing now in the current OS build. I couldn't find such a breakpoint mechanism in Visual Studio or F12 so I wrote a little script to approximate JavaScript data breakpoints.

The script creates a stub object with a getter and setter. It actually performs the get or set but also calls debugger; to break in the debugger. In order to handle my case of needing to break when window.object1.object2 was created or accessed, I further had it recursively set up such stub objects for the matching property names.

Its not perfect because it is an enumerable property and shows up in hasOwnProperty and likely other places. But for your average code that checks for the existence of a property via if (object.property) it works well.

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Tweet from David Risney

2016 Jun 17, 1:04
Podcasters hate going to the post office.
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Tweet from Johnny Xmas

2016 Jun 16, 1:30
::weeps uncontrollably::
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WinRT Toast from PowerShell

2016 Jun 15, 3:54

I've made a PowerShell script to show system toast notifications with WinRT and PowerShell. Along the way I learned several interesting things.

First off calling WinRT from PowerShell involves a strange syntax. If you want to use a class you write [-Class-,-Namespace-,ContentType=WindowsRuntime] first to tell PowerShell about the type. For example here I create a ToastNotification object:

[void][Windows.UI.Notifications.ToastNotification,Windows.UI.Notifications,ContentType=WindowsRuntime];
$toast = New-Object Windows.UI.Notifications.ToastNotification -ArgumentList $xml;
And here I call the static method CreateToastNotifier on the ToastNotificationManager class:
[void][Windows.UI.Notifications.ToastNotificationManager,Windows.UI.Notifications,ContentType=WindowsRuntime];
$notifier = [Windows.UI.Notifications.ToastNotificationManager]::CreateToastNotifier($AppUserModelId);
With this I can call WinRT methods and this is enough to show a toast but to handle the click requires a little more work.

To handle the user clicking on the toast I need to listen to the Activated event on the Toast object. However Register-ObjectEvent doesn't handle WinRT events. To work around this I created a .NET event wrapper class to turn the WinRT event into a .NET event that Register-ObjectEvent can handle. This is based on Keith Hill's blog post on calling WinRT async methods in PowerShell. With the event wrapper class I can run the following to subscribe to the event:

function WrapToastEvent {
param($target, $eventName);

Add-Type -Path (Join-Path $myPath "PoshWinRT.dll")
$wrapper = new-object "PoshWinRT.EventWrapper[Windows.UI.Notifications.ToastNotification,System.Object]";
$wrapper.Register($target, $eventName);
}

[void](Register-ObjectEvent -InputObject (WrapToastEvent $toast "Activated") -EventName FireEvent -Action {
...
});

To handle the Activated event I want to put focus back on the PowerShell window that created the toast. To do this I need to call the Win32 function SetForegroundWindow. Doing so from PowerShell is surprisingly easy. First you must tell PowerShell about the function:

Add-Type @"
using System;
using System.Runtime.InteropServices;
public class PInvoke {
[DllImport("user32.dll")] [return: MarshalAs(UnmanagedType.Bool)]
public static extern bool SetForegroundWindow(IntPtr hwnd);
}
"@
Then to call:
[PInvoke]::SetForegroundWindow((Get-Process -id $myWindowPid).MainWindowHandle);

But figuring out the HWND to give to SetForegroundWindow isn't totally straight forward. Get-Process exposes a MainWindowHandle property but if you start a cmd.exe prompt and then run PowerShell inside of that, the PowerShell process has 0 for its MainWindowHandle property. We must follow up process parents until we find one with a MainWindowHandle:

$myWindowPid = $pid;
while ($myWindowPid -gt 0 -and (Get-Process -id $myWindowPid).MainWindowHandle -eq 0) {
$myWindowPid = (gwmi Win32_Process -filter "processid = $($myWindowPid)" | select ParentProcessId).ParentProcessId;
}
PermalinkComments.net c# powershell toast winrt

Tweet from David Risney

2016 Jun 10, 3:24
@ericlaw So... he doesn't support HTTP2 yet?
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Tweet from Windows Blogs

2016 Jun 10, 3:01
Using Device Portal to view debug logs for UWP http://blogs.windows.com/buildingapps/2016/06/10/using-device-portal-to-view-debug-logs-for-uwp/ 
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Tweet from Philip II

2016 Jun 9, 9:01
Silly Queen Elizabeth thinks her nation secure from our Spanish Armada. We will soon see @lizbet1533 in chains. No naval power. Sad!
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Tweet from David Risney

2016 Jun 9, 4:02
Movie written by algorithm turns out to be hilarious and intense http://arstechnica.com/the-multiverse/2016/06/an-ai-wrote-this-movie-and-its-strangely-moving/ 
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Tweet from David Risney

2016 Jun 9, 3:48
Is this how we find out who Trump wants as his VP? https://twitter.com/7im/status/740670716870156288 
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Tweet from David Risney

2016 Jun 9, 3:26
Trying to avoid regulation? Put a gun on it. You can't regulate that! http://arstechnica.com/tech-policy/2016/06/man-who-built-gun-drone-flamethrower-drone-argues-faa-cant-regulate-him/ 
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Tweet from Rossen Atanassov

2016 Jun 8, 2:59
I recall meetings when we discussed pursuing WebGL... Now we're going open source with it :) https://github.com/MicrosoftEdge/WebGL 
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Tweet from billy eichner

2016 Jun 7, 12:34
I'm ok with a female President AS LONG as she doesn't start busting ghosts.
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Tweet from David Risney

2016 Jun 7, 9:06
@gregwhitworth @alialvi We were all confused because we for sure didn't think they would just be that annoying =)
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Tweet from gregwhitworth

2016 Jun 7, 1:43
Dear @google, please store my answer to this question so I don't see this every time I start a browser session.
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Tweet from David Risney

2016 Jun 6, 10:37
History & design of the biohazard symbol ☣: http://99percentinvisible.org/article/biohazard-symbol-designed-to-be-memorable-but-meaningless/  Creator sends angry letter over sartorial usage
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Tweet from The A.V. Club

2016 Jun 6, 4:50
BuzzFeed backs out of RNC ad deal, citing profound awfulness of Donald Trump http://avc.lu/1t2uiEN 
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Tweet from David Risney

2016 Jun 5, 4:18
@FremyCompany Edge is all about the pawn promotion
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Tweet from David Risney

2016 Jun 5, 4:10
I played Chrome, Edge, FF & IE against each other in WebDriverChess. Edge just beats out Firefox for #1. Results: https://github.com/david-risney/webDriverChess/#browser-face-off 
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Tweet from David Risney

2016 Jun 5, 4:00
@FremyCompany It uses https://github.com/nmrugg/stockfish.js  the asm.js port of the StockFish chess AI (the asm.js part is why Edge wins)
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Tweet from David Risney

2016 Jun 5, 3:55
I finished WebDriverChess https://github.com/david-risney/webDriverChess/ : Two webdriver supporting browsers play a friendly game of chess. pic.twitter.com/axs92w3uF6
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