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Blazor WASM loading progress indicator #26744

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Blazor WASM loading progress indicator #26744

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Blazor WASM loading progress indicator
guardrex Aug 15, 2022
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guardrex Aug 16, 2022
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guardrex Aug 16, 2022
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43 changes: 43 additions & 0 deletions aspnetcore/blazor/fundamentals/startup.md
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Expand Up @@ -714,6 +714,49 @@ In the following examples, a [Content Security Policy (CSP)](https://developer.m

For more information on CSPs, see <xref:blazor/security/content-security-policy>.

## Loading progress indicators

*This section only applies to Blazor WebAssembly apps.*

The Blazor WebAssembly project template contains Scalable Vector Graphics (SVG) and text indicators that show the loading progress of the app.

The progress indicators are implemented with HTML and CSS using two CSS custom properties (variables) provided by Blazor WebAssembly:

* `--blazor-load-percentage`: The percentage of app files loaded.
* `--blazor-load-percentage-text`: The percentage of app files loaded, rounded to the nearest whole number.

Using the preceding CSS variables, you can create custom progress indicators that match the styling of your app.

In the following example:

* `resourcesLoaded` is an instantaneous count of the resources loaded during app startup.
* `totalResources` is the total number of resources to load.

```javascript
const percentage = resourcesLoaded / totalResources * 100;
document.documentElement.style.setProperty(
'--blazor-load-percentage', `${percentage}%`);
document.documentElement.style.setProperty(
'--blazor-load-percentage-text', `"${Math.floor(percentage)}%"`);
```

The progress indicators are implemented in HTML in the `wwwroot/index.html` file:

```html
<svg class="loading-progress">
<circle r="40%" cx="50%" cy="50%" />
<circle r="40%" cx="50%" cy="50%" />
</svg>
<div class="loading-progress-text"></div>
```

To review the Blazor WebAssembly project template markup and styling for the default progress indicators, see the ASP.NET Core reference source:

* [`wwwroot/index.html`](https://github.com/dotnet/aspnetcore/blob/main/src/ProjectTemplates/Web.ProjectTemplates/content/ComponentsWebAssembly-CSharp/Client/wwwroot/index.html)
* [`app.css`](https://github.com/dotnet/aspnetcore/blob/main/src/ProjectTemplates/Web.ProjectTemplates/content/ComponentsWebAssembly-CSharp/Client/wwwroot/css/app.css)

[!INCLUDE[](~/includes/aspnetcore-repo-ref-source-links.md)]

## Additional resources

* [Environments: Set the app's environment](xref:blazor/fundamentals/environments)
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