functions-bindings-return-value.md

title	description	ms.topic	ms.devlang	ms.custom	ms.date	zone_pivot_groups
Using return value from an Azure Function	Learn to manage return values for Azure Functions	reference	csharp, fsharp, java, javascript, powershell, python	devx-track-csharp, devx-track-extended-java, devx-track-js, devx-track-python	07/25/2023	programming-languages-set-functions-lang-workers

Using the Azure Function return value

This article explains how return values work inside a function. In languages that have a return value, you can bind a function output binding to the return value.

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Set the name property in function.json to $return. If there are multiple output bindings, use the return value for only one of them.

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How return values are used depends on the C# mode you're using in your function app:

In-process

In a C# class library, apply the output binding attribute to the method return value. In C# and C# script, alternative ways to send data to an output binding are out parameters and collector objects.

Here's C# code that uses the return value for an output binding, followed by an async example:

[FunctionName("QueueTrigger")]
[return: Blob("output-container/{id}")]
public static string Run([QueueTrigger("inputqueue")]WorkItem input, ILogger log)
{
    string json = string.Format("{{ \"id\": \"{0}\" }}", input.Id);
    log.LogInformation($"C# script processed queue message. Item={json}");
    return json;
}

[FunctionName("QueueTrigger")]
[return: Blob("output-container/{id}")]
public static Task<string> Run([QueueTrigger("inputqueue")]WorkItem input, ILogger log)
{
    string json = string.Format("{{ \"id\": \"{0}\" }}", input.Id);
    log.LogInformation($"C# script processed queue message. Item={json}");
    return Task.FromResult(json);
}

Isolated process

See Output bindings in the .NET worker guide for details and examples.

---

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::: zone pivot="programming-language-javascript"

Here's the output binding in the function.json file:

{
    "name": "$return",
    "type": "blob",
    "direction": "out",
    "path": "output-container/{id}"
}

Here's the JavaScript code:

module.exports = function (context, input) {
    var json = JSON.stringify(input);
    context.log('Node.js script processed queue message', json);
    return json;
}

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Here's the output binding in the function.json file:

{
    "name": "Response",
    "type": "blob",
    "direction": "out",
    "path": "output-container/{blobname}"
}

Here's the PowerShell code that uses the return value for an http output binding:

Push-OutputBinding -Name Response -Value ([HttpResponseContext]@{
    StatusCode = [HttpStatusCode]::OK
    Body = $blobname
    })

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Here's the output binding in the function.json file:

{
    "name": "$return",
    "type": "blob",
    "direction": "out",
    "path": "output-container/{id}"
}

Here's the Python code:

def main(input: azure.functions.InputStream) -> str:
    return json.dumps({
        'name': input.name,
        'length': input.length,
        'content': input.read().decode('utf-8')
    })

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Apply the output binding annotation to the function method. If there are multiple output bindings, use the return value for only one of them.

Here's Java code that uses the return value for an output binding:

@FunctionName("QueueTrigger")
@StorageAccount("AzureWebJobsStorage")
@BlobOutput(name = "output", path = "output-container/{id}")
public static String run(
  @QueueTrigger(name = "input", queueName = "inputqueue") WorkItem input,
  final ExecutionContext context
) {
  String json = String.format("{ \"id\": \"%s\" }", input.id);
  context.getLogger().info("Java processed queue message. Item=" + json);
  return json;
}

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Next steps

[!div class="nextstepaction"] Handle Azure Functions binding errors