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responses.md

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Responses

A router handler function can return different values. Different return values and their consequences are listed here. The return value can be either a Promise or the value itself.

All following handlers set the response body to JSON and set the mime type accordingly.

app.get("/", (ctx) => {
  return {"json": "success"};
});

// is equal to

app.get("/", async (ctx) => {
  return {"json": "success"};
});

// is equal to

app.get("/", (ctx) => {
  return new Promise(resolve => resolve({"json": "success"}));
});

Response Values

  • undefined | void

    The function does not return a value and the body is not changed. The following applicable handler functions are still executed. The body can still be changed using ctx.res.setBody().

  • true

    The body is not changed by this function. The following applicable handler functions are not executed. The body can still be changed using ctx.res.setBody().

  • Uint8Array

    The response body is set to this Uint8Array. If the MIME-Type is not set yet, it will be set to application/octet-stream. The following applicable handler functions are not executed.

  • Deno.Reader

    The response body is set to this Deno.Reader. If the MIME-Type is not set yet, it will be set to application/octet-stream. The following applicable handler functions are not executed.

  • string

    The response body is set to this Deno.Reader. If the MIME-Type is not set yet, it will be set to text/plain. The following applicable handler functions are not executed.

  • any other object ({ [_: string]: any })

    This object will be parsed as string with JSON.parse(). If the MIME-Type is not set yet, it will be set to application/json. The following applicable handler functions are not executed.

Lifecycle

If a return value is set in a lifecycle hook (for example, in onRequest), no further request handlers are executed by this hook (for example, no further onRequest handlers), but the next hook (for example, in this case preParsing) is executed. Therefore, only in the lifecycle hook onHandle should a return value other than undefined be set. This ensures that the request is processed correctly.

To set the body in other handlers, it is recommended to rather use the function ctx.res.setBody() and return undefined or nothing.

If there is still no return value set after the lifecycle hook onHandle, a ClientError (status: 404 Not Found) is thrown.

If a ClientError has been thrown in a lifecycle hook up to and including onHandle, then the status and the body will be set accordingly (status code: e.statusCode). If another error is thrown, the status and body are also set (status code: 500).