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JavaScript Execution Feature

The JavaScript Execution feature lets you execute arbitrary JavaScript in the browser control from C#. This is useful for calling browser APIs, querying DOM state, or running custom scripts.

Contents​

Executing JavaScript​

Execute a JavaScript expression and get the result:

// Execute and get the raw result (JSON-encoded)
string? result = await window.Features.JavaScript.ExecuteJavaScriptAsync(
    "document.title",
    CancellationToken.None
);

// Execute and deserialize to a typed result
string? title = await window.Features.JavaScript.ExecuteJavaScriptAsync<string>(
    "document.title",
    CancellationToken.None
);

int? count = await window.Features.JavaScript.ExecuteJavaScriptAsync<int>(
    "document.querySelectorAll('button').length",
    CancellationToken.None
);

The script parameter is a JavaScript expression. The result is JSON-encoded and deserialized to the requested type. If the expression evaluates to undefined, the result is null.

Returning Values​

The JavaScript expression should evaluate to a JSON-serializable value:

// Primitives
string? text = await window.Features.JavaScript.ExecuteJavaScriptAsync<string>(
    "document.querySelector('h1')?.textContent"
);

bool? isVisible = await window.Features.JavaScript.ExecuteJavaScriptAsync<bool>(
    "document.getElementById('modal')?.style.display !== 'none'"
);

// Objects
var element = await window.Features.JavaScript.ExecuteJavaScriptAsync<JsonElement>(
    "JSON.stringify({ tag: document.body.tagName, childCount: document.body.children.length })"
);

Fire-and-Forget Evaluation​

For scripts where you don't need the result, use SendEvalToBrowser:

window.Features.JavaScript.SendEvalToBrowser("console.log('Hello from C#')");
window.Features.JavaScript.SendEvalToBrowser(
    "document.body.style.backgroundColor = 'red'"
);

The result is sent back via a separate message if a requestId is provided.

Error Handling​

JavaScript evaluation failures throw JavaScriptEvaluationException:

try {
    string? result = await window.Features.JavaScript.ExecuteJavaScriptAsync<string>(
        "undefinedFunction()"
    );
} catch (JavaScriptEvaluationException ex) {
    Console.WriteLine($"JS evaluation failed: {ex.Message}");
}
note

JavaScript execution requires the window to be ready. Use await window.WaitForReadyAsync() before executing scripts if you're calling from a startup path.

See Also​