Scott Hanselman

Updating jQuery-based Lazy Image Loading to IntersectionObserver

April 11, '18 Comments [7] Posted in ASP.NET | HTML5 | Javascript
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The Hanselminutes Tech PodcastFive years ago I implemented "lazy loading" of the 600+ images on my podcast's archives page (I don't like paging, as a rule) over here https://www.hanselminutes.com/episodes. I did it with jQuery and a jQuery Plugin. It was kind of messy and gross from a purist's perspective, but it totally worked and has easily saved me (and you) hundreds of dollars in bandwidth over the years. The page is like 9 or 10 megs if you load 600 images, not to mention you're loading 600 freaking images.

Fast-forward to 2018, and there's the "Intersection Observer API" that's supported everywhere but Safari and IE, well, because, Safari and IE, sigh. We will return to that issue in a moment.

Following Dean Hume's blog post on the topic, I start with my images like this. I don't populate src="", but instead hold the Image URL in the HTML5 data- bucket of data-src. For src, I can use the nothing grey.gif or just style and color the image grey.

<a href="/626/christine-spangs-open-source-journey-from-teen-oss-contributor-to-cto-of-nylas" class="showCard">
    <img data-src="https://images.hanselminutes.com/images/626.jpg" 
         class="lazy" src="/images/grey.gif" width="212" height="212" alt="Christine Spang&#x27;s Open Source Journey from Teen OSS Contributor to CTO of Nylas" />
    <span class="shownumber">626</span>                
    <div class="overlay title">Christine Spang&#x27;s Open Source Journey from Teen OSS Contributor to CTO of Nylas</div>
</a>
<a href="/625/a-new-sega-megadrivegenesis-game-in-2018-with-1995-tools-with-tanglewoods-matt-phillips" class="showCard">
    <img data-src="https://images.hanselminutes.com/images/625.jpg" 
         class="lazy" src="/images/grey.gif" width="212" height="212" alt="A new Sega Megadrive/Genesis Game in 2018 with 1995 Tools with Tanglewood&#x27;s Matt Phillips" />
    <span class="shownumber">625</span>                
    <div class="overlay title">A new Sega Megadrive/Genesis Game in 2018 with 1995 Tools with Tanglewood&#x27;s Matt Phillips</div>
</a>

Then, if the images get within 50px intersecting the viewPort (I'm scrolling down) then I load them:

// Get images of class lazy
const images = document.querySelectorAll('.lazy');
const config = {
  // If image gets within 50px go get it
  rootMargin: '50px 0px',
  threshold: 0.01
};

let observer = new IntersectionObserver(onIntersection, config);
  images.forEach(image => {
    observer.observe(image);
  });

Now that we are watching it, we need to do something when it's observed.

function onIntersection(entries) {
  // Loop through the entries
  entries.forEach(entry => {
    // Are we in viewport?
    if (entry.intersectionRatio > 0) {

      // Stop watching and load the image
      observer.unobserve(entry.target);
      preloadImage(entry.target);
    }
  });
}

If the browser (IE, Safari, Mobile Safari) doesn't support IntersectionObserver, we can do a few things. I *could* fall back to my old jQuery technique, although it would involve loading a bunch of extra scripts for those browsers, or I could just load all the images in a loop, regardless, like:

if (!('IntersectionObserver' in window)) {
    loadImagesImmediately(images);
} else {...}

Dean's examples are all "Vanilla JS" and require no jQuery, no plugins, no polyfills WITH browser support. There are also some IntersectionObserver helper libraries out there like Cory Dowdy's IOLazy. Cory's is a nice simple wrapper and is super easy to implement. Given I want to support iOS Safari as well, I am using a polyfill to get the support I want from browsers that don't have it natively.

<!-- intersection observer polyfill -->
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=IntersectionObserver"></script>

Polyfill.io is a lovely site that gives you just the fills you need (or those you need AND request) tailored to your browser. Try GETting the URL above in Chrome. You'll see it's basically empty as you don't need it. Then hit it in IE, and you'll get the polyfill. The official IntersectionObserver polyfill is at the w3c.

At this point I've removed jQuery entirely from my site and I'm just using an optional polyfill plus browser support that didn't exist when I started my podcast site. Fewer moving parts means a cleaner, leaner, simpler site!

Go subscribe to the Hanselminutes Podcast today! We're on iTunes, Spotify, Google Play, and even Twitter!


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Optimizing an ASP.NET Core site with Chrome's Lighthouse Auditor

April 5, '18 Comments [5] Posted in ASP.NET | DotNetCore
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I'm continuing to update my podcast site. I've upgraded it from ASP.NET "Web Pages" (10 year old code written in WebMatrix) to ASP.NET Core 2.1 developed with VS Code. Here's some recent posts:

I was talking with Ire Aderinokun today for an upcoming podcast episode and she mentioned I should use Lighthouse (It's built into Chrome, can be run as an extension, or run from the command line) to optimize my podcast site. I, frankly, had not looked at that part of Chrome in a long time and was shocked and how powerful it was!

Performance 73, PWA 55, Accessbiolity 68, Best Practices 81, SEO 78

Lighthouse also told me that I was using an old version of jQuery (I know that) that had known security issues (I didn't know that!)

It told me about Accessibility issues as well, pointing out that some of my links were not discernable to a screen reader.

Some of these issues were/are easily fixed in minutes. I think I spent about 20 minutes fixing up some links, compressing a few images, and generally "tidying up" in ways that I knew wouldn't/shouldn't break my site. Those few minutes took my Accessibility and Best Practices score up measurably, but I clearly have some work to do around Performance. I never even considered my Podcast Site as a potential Progressive Web App (PWA) but now that I have a new podcast host and a nice embedded player, that may be a possibility for the future!

Performance 73, PWA 55, Accessbiolity 85, Best Practices 88, SEO 78

My largest issue is with my (aging) CSS. I'd like to convert the site to use FlexBox or a CSS Grid as well as fixed up my Time to First Meaningful Paint.

I went and updated my Archives page a while back with Lazy Image loading, but it was using jQuery and some older (4+ year old) techniques. I'll revisit those with modern techniques AND apply them to the grid of 16 shows on the site's home page as well.

There are opportunities to speed up my application using offscreen images

I have only just begun but I'll report back as I speed things up!

What tools do YOU use to audit your websites?


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Audio Switcher should be built into Windows - Easily Switch Playback and Recording Devices

April 4, '18 Comments [21] Posted in Tools
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Audio SwitcherI've been running a podcast now for over 600 episodes and I do most of my recordings here at home using a Peavey PV6 Mixing Console - it's fantastic. However, I also work remotely and use Skype a lot to talk to co-workers. Sometimes I use a USB Headset but I also have a Polycom Work Phone for conference calls. Plus my webcams have microphones, so all this adds up to a lot of audio devices.

Windows 10 improved the switching experience for Playback Devices, but there's no "two click" way to quickly change Recording Devices. A lot of Sound Settings are moving into the Windows 10 Settings App but it's still incomplete and sometimes you'll find yourself looking at the older Sound Dialog:

Sound Control Panel

Enter David Kean's "Audio Switcher." It's nearly 3 years old with source code on GitHub, but it works AMAZINGLY. It's literally what the Power User has always wanted when managing audio on Windows 10.

UPDATED NOTE: Turns out there are SEVERAL Windows Audio Switchers out there in the world, and they are all lovely. Also check out the more feature-ful Audio Switcher from Sean Chapman at https://audioswit.ch/er with code at https://github.com/xenolightning/AudioSwitcher_v1!

It adds a Headphone Icon in the Tray, and clicking it on puts the Speakers at the Top and Mics at the Bottom. Right-clicking an item lets you set it as default. Even nicer if you set the icons for your devices like I did.

Audio Switcher

Ok, that's the good news. It's great, and there's Source Code available so you can build it easily with free Visual Studio Community.

Bad news? Today, there's no "release" or ZIP or EXE file for you to download. That said, I uploaded a totally unsupported and totally not my responsibility and you shouldn't trust me compiled version here.

Hopefully after this blog post is up a few days, David will see this blog post and make an installer with a cert and/or put this wonderful utility somewhere, as folks clearly are interested. I'll update this blog post as soon as more people start using Audio Switcher.

Thank you David for making this fantastic utility!


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Easier functional and integration testing of ASP.NET Core applications

March 30, '18 Comments [11] Posted in ASP.NET | DotNetCore
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.NET Test ExplorerIn ASP.NET 2.1 (now in preview) there's apparently a new package called Microsoft.AspNetCore.Mvc.Testing that's meant to help streamline in-memory end-to-end testing of applications that use the MVC pattern. I've been re-writing my podcast site at https://hanselminutes.com in ASP.NET Core 2.1 lately, and recently added some unit testing and automatic unit testing with code coverage. Here's a couple of basic tests. Note that these call the Razor Pages directly and call their OnGet() methods directly. This shows how ASP.NET Core is nicely factored for Unit Testing but it doesn't do a "real" HTTP GET or perform true end-to-end testing.

These tests are testing if visiting URLs like /620 will automatically redirect to the correct full canonical path as they should.

[Fact]
public async void ShowDetailsPageIncompleteTitleUrlTest()
{
// FAKE HTTP GET "/620"
IActionResult result = await pageModel.OnGetAsync(id:620, path:"");

RedirectResult r = Assert.IsType<RedirectResult>(result);
Assert.NotNull(r);
Assert.True(r.Permanent); //HTTP 301?
Assert.Equal("/620/jessica-rose-and-the-worst-advice-ever",r.Url);
}

[Fact]
public async void SuperOldShowTest()
{
// FAKE HTTP GET "/default.aspx?showId=18602"
IActionResult result = await pageModel.OnGetOldShowId(18602);

RedirectResult r = Assert.IsType<RedirectResult>(result);
Assert.NotNull(r);
Assert.True(r.Permanent); //HTTP 301?
Assert.StartsWith("/615/developing-on-not-for-a-nokia-feature",r.Url);
}

I wanted to see how quickly and easily I could do these same two tests, except "from the outside" with an HTTP GET, thereby testing more of the stack.

I added a reference to Microsoft.AspNetCore.Mvc.Testing in my testing assembly using the command-line equivalanet of "Right Click | Add NuGet Package" in Visual Studio. This CLI command does the same thing as the UI and adds the package to the csproj file.

dotnet add package Microsoft.AspNetCore.Mvc.Testing -v 2.1.0-preview1-final

It includes a new WebApplicationTestFixture that I point to my app's Startup class. Note that I can take store the HttpClient the TestFixture makes for me.

public class TestingMvcFunctionalTests : IClassFixture<WebApplicationTestFixture<Startup>>
{
public HttpClient Client { get; }

public TestingMvcFunctionalTests(WebApplicationTestFixture<Startup> fixture)
{
Client = fixture.Client;
}
}

No tests yet, just setup. I'm using SSL redirection so I'll make sure the client knows that, and add a test:

public TestingMvcFunctionalTests(WebApplicationTestFixture<Startup> fixture)
{
Client = fixture.Client;
Client.BaseAddress = new Uri("https://localhost");
}

[Fact]
public async Task GetHomePage()
{
// Arrange & Act
var response = await Client.GetAsync("/");

// Assert
Assert.Equal(HttpStatusCode.OK, response.StatusCode);
}

This will fail, in fact. Because I have an API Key that is needed to call out to my backend system, and I store it in .NET's User Secrets system. My test will get an InternalServerError instead of OK.

Starting test execution, please wait...
[xUnit.net 00:00:01.2110048] Discovering: hanselminutes.core.tests
[xUnit.net 00:00:01.2690390] Discovered: hanselminutes.core.tests
[xUnit.net 00:00:01.2749018] Starting: hanselminutes.core.tests
[xUnit.net 00:00:08.1088832] hanselminutes_core_tests.TestingMvcFunctionalTests.GetHomePage [FAIL]
[xUnit.net 00:00:08.1102884] Assert.Equal() Failure
[xUnit.net 00:00:08.1103719] Expected: OK
[xUnit.net 00:00:08.1104377] Actual: InternalServerError
[xUnit.net 00:00:08.1114432] Stack Trace:
[xUnit.net 00:00:08.1124268] D:\github\hanselminutes-core\hanselminutes.core.tests\FunctionalTests.cs(29,0): at hanselminutes_core_tests.TestingMvcFunctionalTests.<GetHomePage>d__4.MoveNext()
[xUnit.net 00:00:08.1126872] --- End of stack trace from previous location where exception was thrown ---
[xUnit.net 00:00:08.1158250] Finished: hanselminutes.core.tests
Failed hanselminutes_core_tests.TestingMvcFunctionalTests.GetHomePage
Error Message:
Assert.Equal() Failure
Expected: OK
Actual: InternalServerError

Where do these secrets come from? In Development they come from user secrets.

public Startup(IHostingEnvironment env)
{
this.env = env;
var builder = new ConfigurationBuilder();

if (env.IsDevelopment())
{
builder.AddUserSecrets<Startup>();
}
Configuration = builder.Build();
}

But in Production they come from the ENVIRONMENT. Are these tests Development or Production...I must ask myself.  They are Production unless told otherwise. I can override the Fixture and tell it to use another Environment, like "Development." Here is a way (given this preview) to make my own TestFixture by deriving and grabbing and override to change the Environment. I think it's too hard and should be easier.

Either way, the real question here is for me - do I want my tests to be integration tests in development or in "production." Likely I need to make a new environment for myself - "testing."

public class MyOwnTextFixture<TStartup> : WebApplicationTestFixture<Startup> where TStartup : class
{
public MyOwnTextFixture() { }

protected override void ConfigureWebHost(IWebHostBuilder builder)
{
builder.UseEnvironment("Development");
}
}

However, my User Secrets still aren't loading, and that's where the API Key is that I need.

BUG?: There is either a bug here, or I don't know what I'm doing. I'm loading User Secrets in builder.AddUserSecrets<Startup> and later injecting the IConfiguration instance from builder.Build() and going "_apiKey = config["SimpleCastAPIKey"];" but it's null. The config that's injected later in the app isn't the same one that's created in Startup.cs. It's empty. Not sure if this is an ASP.NE Core 2.0 thing or 2.1 thing but I'm going to bring it up with the team and update this blog post later. It might be a Razor Pages subtlety I'm missing.
For now, I'm going to put in a check and manually fix up my Config. However, when this is fixed (or I discover my error) this whole thing will be a pretty nice little set up for integration testing.

I will add another test, similar to the redirect Unit Test but a fuller integration test that actually uses HTTP and tests the result.

[Fact]
public async Task GetAShow()
{
// Arrange & Act
var response = await Client.GetAsync("/620");

// Assert
Assert.Equal(HttpStatusCode.MovedPermanently, response.StatusCode);
Assert.Equal("/620/jessica-rose-and-the-worst-advice-ever",response.Headers.Location.ToString());
}

There's another issue here that I don't understand. Because have to set Client.BaseAddress to https://localhost (because https) and the Client is passed into fixture.Client, I can't set the Base address twice or I'll get an exception, as the Test's Constructor runs twice, but the HttpClient that's passed in as a lifecycler that's longer. It's being reused, and it fails when setting its BaseAddress twice.

Error Message:
System.InvalidOperationException : This instance has already started one or more requests. Properties can only be modified before sending the first request.

BUG? So to work around it I check to see if I've done it before. Which is gross. I want to set the BaseAddress once, but I am not in charge of the creation of this HttpClient as it's passed in by the Fixture.

public TestingMvcFunctionalTests(MyOwnTextFixture<Startup> fixture)
{
Client = fixture.Client;
if (Client.BaseAddress.ToString().StartsWith("https://") == false)
Client.BaseAddress = new Uri("https://localhost");
}

Another option is that I create a new client every time, which is less efficient and perhaps a better idea as it avoids any side effects from other tests, but also feels weird that I should have to do this, as the new standard for ASP.NET Core sites is to be SSL/HTTPS by default..

public TestingMvcFunctionalTests(MyOwnTextFixture<Startup> fixture)
{
Client = fixture.CreateClient(new Uri(https://localhost));
}

I'm still learning about how it all fits together, but later I plan to add in Selenium tests to have a full, complete, test suite that includes the browser, CSS, JavaScript, end-to-end integration tests, and unit tests.

Let me know if you think I'm doing something wrong. This is preview stuff, so it's early days!


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Command line "tab" completion for .NET Core CLI in PowerShell or bash

March 27, '18 Comments [14] Posted in DotNetCore
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Lots of people are using open source .NET Core and the "dotnet" command line, but few know that the .NET CLI supports command "tab" completion!

You can ensure you have it on .NET Core 2.0 with this test:

C:\Users\scott>  dotnet complete "dotnet add pac"
package

You can see I do, as it proposed "package" as the completion for "pac"

Now, just go into PowerShell and run:

notepad $PROFILE

And add this code to the bottom to register "dotnet complete" as the "argument completer" for the dotnet command.

# PowerShell parameter completion shim for the dotnet CLI 
Register-ArgumentCompleter -Native -CommandName dotnet -ScriptBlock {
    param($commandName, $wordToComplete, $cursorPosition)
        dotnet complete --position $cursorPosition "$wordToComplete" | ForEach-Object {
           [System.Management.Automation.CompletionResult]::new($_, $_, 'ParameterValue', $_)
        }
}

Then just use it! You can do the same not only in PowerShell, but in bash, or zsh as well!

It's super useful for "dotnet add package" because it'll make smart completions like this:

It also works for adding/removing local project preferences as it is project file aware. Go set it up NOW, it'll take you 3 minutes.

RANDOM BUT ALSO USEFUL: "dotnet serve" - A simple command-line HTTP server.

Here's a useful little global tool - dotnet serve. It launches a server in the current working directory and serves all files in it. It's not kestrel, the .NET Application/Web Server. It's just a static webserver for development.

The latest release of dotnet-serve requires the 2.1.300-preview1 .NET Core SDK or newer. Once installed, run this command:

dotnet install tool --global dotnet-serve 

Then whenever I'm in a folder where I want to server something static (CSS, JS, PNGs, whatever) I can just

dotnet serve

It can also optionally open a web browser navigated to that localhost URL.

NOTE: Here's a growing list of .NET Global Tools.


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.