---
title: Sheets in Blazor Sites
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[Blazor](https://dotnet.microsoft.com/en-us/apps/aspnet/web-apps/blazor) is a
framework for building user interfaces using C#, HTML, JS and CSS.

[SheetJS](https://sheetjs.com) is a JavaScript library for reading and writing
data from spreadsheets.

This demo uses Blazor and SheetJS to process and generate spreadsheets. We'll
explore how to load SheetJS in Razor components and compare common state models
and data flow strategies.

:::caution Blazor support is considered experimental.

Great open source software grows with user tests and reports. Any issues should
be reported to the Blazor project for further diagnosis.

:::

:::danger Telemetry

**The `dotnet` command embeds telemetry.**

The `DOTNET_CLI_TELEMETRY_OPTOUT` environment variable should be set to `1`.

["Platform Configuration"](#platform-configuration) includes instructions for
setting the environment variable on supported platforms.

:::

## Integration Details

### Installation

The SheetJS library can be loaded when the page is loaded or imported whenever
the library functionality is used.

#### Standalone Script

The [SheetJS Standalone scripts](/docs/getting-started/installation/standalone)
can be loaded in the root HTML page (typically `wwwroot/index.html`):

<CodeBlock language="html">{`\
<!-- use version ${current} -->
<script lang="javascript" src="https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js"></script>`}
</CodeBlock>

#### ECMAScript Module

The SheetJS ECMAScript module script can be dynamically imported from functions.
This ensures the library is only loaded when necessary. The following example
loads the library and returns a Promise that resolves to the version string:

<CodeBlock language="js">{`\
async function sheetjs_version(id) {
  /* dynamically import the script in the event listener */
  // highlight-next-line
  const XLSX = await import("https://cdn.sheetjs.com/xlsx-${current}/package/xlsx.mjs");
\n\
  /* use the library */
  return XLSX.version;
}`}
</CodeBlock>

### Calling JS from C#

#### Setup

The primary mechanism for invoking JS functions from Blazor is `IJSRuntime`[^1].
It should be injected at the top of relevant Razor component scripts:

```csharp title="Injecting IJSRuntime"
@inject IJSRuntime JS
```

#### Fire and Forget

When exporting a file with the SheetJS `writeFile` method[^2], browser APIs do
not provide success or error feedback. As a result, this demo invokes functions
using the `InvokeVoidAsync` static method[^3]:

```csharp title="Invoking JS functions from C#"
private async Task ExportDataset() {
    await JS.InvokeVoidAsync("export_method", data);
}
```

Methods are commonly bound to buttons in the Razor template using `@onclick`:

```html title="Binding callback to a HTML button"
<button @onclick="ExportDataset">Export Dataset</button>
```

### State in Blazor

The example [presidents sheet](https://docs.sheetjs.com/pres.xlsx) has one
header row with "Name" and "Index" columns.

![`pres.xlsx` data](pathname:///pres.png)

#### C# Representation

The natural C# representation of a single row is a class object:

```csharp title="President class"
public class President {
  public string Name { get; set; }
  public int Index { get; set; }
}

var PrezClinton = new President() { Name = "Bill Clinton", Index = 42 };
```

The entire dataset is typically stored in an array of class objects:

```csharp title="President dataset"
private President[] data;
```

#### Data Interchange

`InvokeVoidAsync` can pass data from the C# state to a JS function:

```csharp
    await JS.InvokeVoidAsync("export_method", data);
```

Each row in the dataset will be passed as a separate argument to the JavaScript
method, so the JavaScript code should collect the arguments:

```js title="Collecting rows in a JS callback"
/* NOTE: blazor spreads the C# array, so the ... spread syntax is required */
async function export_method(...rows) {
  /* display the array of objects */
  console.log(rows);
}
```

Each row is a simple JavaScript object.

:::caution pass

Blazor automatically spreads arrays. Each row is passed as a separate argument
to the JavaScript method.

The example method uses the JavaScript spread syntax to collect the arguments.

:::

#### Exporting Data

With the collected array of objects, the SheetJS `json_to_sheet` method[^4] will
generate a SheetJS worksheet[^5] from the dataset. After creating a workbook[^6]
object with the `book_new` method[^7], the file is written with `writeFile`[^2]:

<CodeBlock title="JS Callback for exporting datasets" language="javascript">{`\
/* NOTE: blazor spreads the C# array, so the spread is required */
async function export_method(...rows) {
  const XLSX = await import("https://cdn.sheetjs.com/xlsx-${current}/package/xlsx.mjs");
  const ws = XLSX.utils.json_to_sheet(rows);
  const wb = XLSX.utils.book_new(ws, "Data");
  XLSX.writeFile(wb, "SheetJSBlazor.xlsx");
}`}
</CodeBlock>


### HTML Tables

When displaying datasets, Razor components typically generate HTML tables:

```html title="Razor template from official starter"
<table class="table" id="weather-table">
  <thead>
    <tr><th>Date</th><th>Temp. (C)</th><th>Temp. (F)</th><th>Summary</th></tr>
  </thead>
  <tbody>
    @foreach (var forecast in forecasts)
    {
      <tr>
        <td>@forecast.Date.ToShortDateString()</td>
        <td>@forecast.TemperatureC</td>
        <td>@forecast.TemperatureF</td>
        <td>@forecast.Summary</td>
      </tr>
    }
  </tbody>
</table>
```

If it has an `id`, JS code on the frontend can find the table element using the
`document.getElementById` DOM method. A SheetJS workbook object can be generated
using the `table_to_book` method[^8] and exported with `writeFile`[^2]:

<CodeBlock title="JS Callback for exporting HTML TABLE elements" language="javascript">{`\
/* NOTE: blazor spreads the C# array, so the spread is required */
async function export_method() {
  const XLSX = await import("https://cdn.sheetjs.com/xlsx-${current}/package/xlsx.mjs");
  const wb = XLSX.utils.table_to_book(document.getElementById("weather-table"));
  XLSX.writeFile(wb, "SheetJSBlazor.xlsx");
}`}
</CodeBlock>

This approach uses data that already exists in the document, so no additional
data is passed from C# to JavaScript.

## Complete Demo

The Blazor + WASM starter app includes a "Weather" component that displays data
from a C#-managed dataset. This demo uses SheetJS to export data in two ways:

- "Export Dataset" will send row objects from the underlying C# data store to
  the frontend. The SheetJS `json_to_sheet` method[^4] builds the worksheet.

- "Export HTML Table" will scrape the table using the SheetJS `table_to_book`
  method[^8]. No extra data will be sent to the frontend.

:::note Tested Deployments

This demo was tested in the following deployments:

| Architecture | Date       |
|:-------------|:-----------|
| `darwin-arm` | 2024-10-15 |

:::

### Platform Configuration

0) Set the `DOTNET_CLI_TELEMETRY_OPTOUT` environment variable to `1`.

<details open>
  <summary><b>How to disable telemetry</b> (click to hide)</summary>

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

Add the following line to `.profile`, `.bashrc` and `.zshrc`:

```bash title="(add to .profile , .bashrc , and .zshrc)"
export DOTNET_CLI_TELEMETRY_OPTOUT=1
```

Close and restart the Terminal to load the changes.

  </TabItem>
  <TabItem value="win" label="Windows">

Type `env` in the search bar and select "Edit the system environment variables".

In the new window, click the "Environment Variables..." button.

In the new window, look for the "System variables" section and click "New..."

Set the "Variable name" to `DOTNET_CLI_TELEMETRY_OPTOUT` and the value to `1`.

Click "OK" in each window (3 windows) and restart your computer.

  </TabItem>
</Tabs>

</details>

1) Install .NET

<details>
  <summary><b>Installation Notes</b> (click to show)</summary>

For macOS x64 and ARM64, install the `dotnet-sdk` Cask with Homebrew:

```bash
brew install --cask dotnet-sdk
```

For Steam Deck Holo and other Arch Linux x64 distributions, the `dotnet-sdk` and
`dotnet-runtime` packages should be installed using `pacman`:

```bash
sudo pacman -Syu dotnet-sdk dotnet-runtime
```

https://dotnet.microsoft.com/en-us/download/dotnet/6.0 is the official source
for Windows and ARM64 Linux versions.

</details>

2) Open a new Terminal window in macOS or PowerShell window in Windows.

### App Creation

3) Create a new `blazorwasm` app:

```bash
dotnet new blazorwasm -o SheetJSBlazorWasm
cd SheetJSBlazorWasm
dotnet run
```

When the Blazor service runs, the terminal will display a URL:

```text
info: Microsoft.Hosting.Lifetime[14]
// highlight-next-line
      Now listening on: http://localhost:6969
```

4) In a new browser window, open the displayed URL from Step 3.

5) Click the "Weather" link and confirm the page includes a data table.

6) Stop the server (press <kbd>CTRL</kbd>+<kbd>C</kbd> in the terminal window).

### SheetJS Integration

7) Add the following script tag to `wwwroot/index.html` in the `HEAD` block:

<CodeBlock title="wwwroot/index.html (add within the HEAD block)" language="html">{`\
<script>
/* NOTE: blazor spreads the C# array, so the spread is required */
async function export_dataset(...rows) {
  const XLSX = await import("https://cdn.sheetjs.com/xlsx-${current}/package/xlsx.mjs");
  const ws = XLSX.utils.json_to_sheet(rows);
  const wb = XLSX.utils.book_new(ws, "Data");
  XLSX.writeFile(wb, "SheetJSBlazorDataset.xlsx");
}
\n\
async function export_html(id) {
  const XLSX = await import("https://cdn.sheetjs.com/xlsx-${current}/package/xlsx.mjs");
  const wb = XLSX.utils.table_to_book(document.getElementById(id));
  XLSX.writeFile(wb, "SheetJSBlazorHTML.xlsx");
}
</script>`}
</CodeBlock>

8) Inject the `IJSRuntime` dependency near the top of `Pages/Weather.razor`:

```csharp title="Pages/Weather.razor (add highlighted lines)"
@page "/weather"
@inject HttpClient Http
// highlight-next-line
@inject IJSRuntime JS
```

9) Add an ID to the `TABLE` element in `Pages/Weather.razor`:

```html title="Pages/Weather.razor (add id to TABLE element)"
{
    <!-- highlight-next-line -->
    <table class="table" id="weather-table">
        <thead>
            <tr>
```

10) Add callbacks to the `@code` section in `Pages/Weather.razor`:

```csharp title="Pages/Weather.razor (add within the @code section)"
    private async Task ExportDataset()
    {
        await JS.InvokeVoidAsync("export_dataset", forecasts);
    }

    private async Task ExportHTML()
    {
        await JS.InvokeVoidAsync("export_html", "weather-table");
    }
```

11) Add Export buttons to the template in `Pages/Weather.razor`:

```csharp title="Pages/Weather.razor (add highlighted lines)"
<p>This component demonstrates fetching data from the server.</p>

<!-- highlight-start -->
<button @onclick="ExportDataset">Export Dataset</button>
<button @onclick="ExportHTML">Export HTML TABLE</button>
<!-- highlight-end -->
```


### Testing

12) Launch the `dotnet` process again:

```bash
dotnet run
```

When the Blazor service runs, the terminal will display a URL:

```text
info: Microsoft.Hosting.Lifetime[14]
      Now listening on: http://localhost:6969
```

13) In a new browser window, open the displayed URL from Step 12.

14) Click the "Weather" link. The page should match the following screenshot:

![SheetJSBlazorWasm with Exports](pathname:///blazor/weather.png)

15) Click the "Export Dataset" button and save the generated file to
`SheetJSBlazorDataset.xlsx`. Open the file in a spreadsheet editor and confirm
the data matches the table. The column labels will differ since the underlying
dataset uses different labels.

![SheetJSBlazorDataset.xlsx](pathname:///blazor/dataset.png)

16) Click the "Export HTML TABLE" button and save the generated file to
`SheetJSBlazorHTML.xlsx`. Open the file in a spreadsheet editor and confirm the
data matches the table. The column labels will match the HTML table.

![SheetJSBlazorHTML.xlsx](pathname:///blazor/html.png)

:::note pass

It is somewhat curious that the official `dotnet` Blazor sample dataset marks
`1 C` and `-13 C` as "freezing" but marks `-2 C` as "chilly". It stands to
reason that `-2 C` should also be freezing.

:::

[^1]: See ["Microsoft.JSInterop.IJSRuntime"](https://learn.microsoft.com/en-us/dotnet/api/microsoft.jsinterop.ijsruntime) in the `dotnet` documentation.
[^2]: See [`writeFile` in "Writing Files"](/docs/api/write-options)
[^3]: See ["Microsoft.JSInterop.JSRuntimeExtensions.InvokeVoidAsync"](https://learn.microsoft.com/en-us/dotnet/api/microsoft.jsinterop.jsruntimeextensions.invokevoidasync) in the `dotnet` documentation.
[^4]: See [`json_to_sheet` in "Utilities"](/docs/api/utilities/array#array-of-objects-input)
[^5]: See ["Sheet Objects"](/docs/csf/sheet)
[^6]: See ["Workbook Object"](/docs/csf/book)
[^7]: See [`book_new` in "Utilities"](/docs/api/utilities/wb)
[^8]: See [`table_to_book` in "HTML" Utilities](/docs/api/utilities/html#create-new-sheet)