response

The response object is used to send HTTP responses back to the client. It is passed as the third parameter to your mim handler.

mimikModule.exports = (context, request, response) => {
    // Use response to send data back
    response.end('Hello World!');
};

---

Properties

Property	Type	Default	Description
statusCode	number	200	HTTP status code to send

Methods

Method	Description
setHeader(key, value)	Set a response header
write(content)	Write to response stream (for streaming)
end(body)	Send response and close connection
writeMimeFile(filePath, mimeType)	Send a file as response

---

statusCode

Set the HTTP status code before calling end() or write().

app.get('/user/:id', (request, response) => {
    var user = context.storage.getItem('user:' + request.params.id);

    if (!user) {
        response.statusCode = 404;
        response.end('User not found');
        return;
    }

    response.end(user);
});

Common Status Codes

// Success
response.statusCode = 200;  // OK
response.statusCode = 201;  // Created
response.statusCode = 204;  // No Content

// Client errors
response.statusCode = 400;  // Bad Request
response.statusCode = 401;  // Unauthorized
response.statusCode = 403;  // Forbidden
response.statusCode = 404;  // Not Found
response.statusCode = 409;  // Conflict
response.statusCode = 422;  // Unprocessable Entity

// Server errors
response.statusCode = 500;  // Internal Server Error
response.statusCode = 502;  // Bad Gateway
response.statusCode = 503;  // Service Unavailable

---

setHeader()

Sets an HTTP response header.

response.setHeader(key, value) → boolean

Parameter	Type	Description
key	string	Header name
value	string	Header value

Returns: true on success.

app.get('/data', (request, response) => {
    response.setHeader('Content-Type', 'application/json');
    response.setHeader('Cache-Control', 'no-cache');
    response.setHeader('X-Custom-Header', 'custom-value');
    response.end(JSON.stringify({ data: 'value' }));
});

Common Headers

// Content type
response.setHeader('Content-Type', 'application/json');
response.setHeader('Content-Type', 'text/html');
response.setHeader('Content-Type', 'text/plain');

// Caching
response.setHeader('Cache-Control', 'no-cache');
response.setHeader('Cache-Control', 'max-age=3600');

// CORS
response.setHeader('Access-Control-Allow-Origin', '*');
response.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE');
response.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');

// Download
response.setHeader('Content-Disposition', 'attachment; filename="report.pdf"');

---

write()

Writes data to the response stream without closing the connection. Use for streaming responses.

response.write(content) → boolean

Parameter	Type	Description
content	string	Content to write

Returns: true on success.

Throws: Error if client disconnected.

app.get('/stream', (request, response) => {
    response.setHeader('Content-Type', 'text/plain');

    response.write('Starting...\n');
    response.write('Processing step 1...\n');
    response.write('Processing step 2...\n');
    response.write('Done!\n');

    response.end();
});

Server-Sent Events (SSE)

app.get('/events', (request, response) => {
    response.setHeader('Content-Type', 'text/event-stream');
    response.setHeader('Cache-Control', 'no-cache');
    response.setHeader('Connection', 'keep-alive');

    // Send events
    response.write('data: {"event": "connected"}\n\n');
    response.write('data: {"event": "update", "value": 1}\n\n');
    response.write('data: {"event": "update", "value": 2}\n\n');

    response.end();
});

---

end()

Sends the response body and closes the connection.

response.end(body) → boolean

Parameter	Type	Description
body	string	Response body content (optional)

Returns: true on success.

Simple Response

app.get('/', (request, response) => {
    response.end('Hello World!');
});

JSON Response

app.get('/data', (request, response) => {
    response.setHeader('Content-Type', 'application/json');
    response.end(JSON.stringify({
        status: 'ok',
        data: { key: 'value' }
    }));
});

Empty Response

app.delete('/resource/:id', (request, response) => {
    // Delete resource...
    response.statusCode = 204;
    response.end();  // No body
});

Error Response

app.get('/user/:id', (request, response) => {
    var user = context.storage.getItem('user:' + request.params.id);

    if (!user) {
        response.statusCode = 404;
        response.setHeader('Content-Type', 'application/json');
        response.end(JSON.stringify({
            error: 'Not Found',
            message: 'User does not exist'
        }));
        return;
    }

    response.setHeader('Content-Type', 'application/json');
    response.end(user);
});

---

writeMimeFile()

Sends a file as the response with the specified MIME type.

response.writeMimeFile(filePath, mimeType) → boolean

Parameter	Type	Description
filePath	string	Path to the file
mimeType	string	MIME type of the file

Returns: true on success.

Serving Images

app.get('/photo/:id', (request, response) => {
    var photoPath = '/data/photos/' + request.params.id + '.jpg';
    response.writeMimeFile(photoPath, 'image/jpeg');
});

File Download

app.get('/download/:filename', (request, response) => {
    var filename = request.params.filename;
    var filePath = '/data/files/' + filename;

    response.setHeader('Content-Disposition', 'attachment; filename="' + filename + '"');
    response.writeMimeFile(filePath, 'application/octet-stream');
});

Common MIME Types

Extension	MIME Type
.json	application/json
.pdf	application/pdf
.zip	application/zip
.jpg, .jpeg	image/jpeg
.png	image/png
.gif	image/gif
.svg	image/svg+xml
.html	text/html
.css	text/css
.js	application/javascript
.txt	text/plain
.xml	application/xml
.mp3	audio/mpeg
.mp4	video/mp4

---

Common Patterns

JSON API Response

function sendJson(response, statusCode, data) {
    response.statusCode = statusCode;
    response.setHeader('Content-Type', 'application/json');
    response.end(JSON.stringify(data));
}

app.get('/users', (request, response) => {
    var users = [];
    context.storage.eachItemByTag('users', function(key, value) {
        users.push(JSON.parse(value));
        return true;
    });

    sendJson(response, 200, { data: users });
});

app.post('/users', (request, response) => {
    var user = JSON.parse(request.body);
    context.storage.setItemWithTag('user:' + user.id, JSON.stringify(user), 'users');

    sendJson(response, 201, { created: true, id: user.id });
});

Error Handler

function sendError(response, statusCode, message) {
    response.statusCode = statusCode;
    response.setHeader('Content-Type', 'application/json');
    response.end(JSON.stringify({
        error: true,
        code: statusCode,
        message: message
    }));
}

app.get('/user/:id', (request, response) => {
    var user = context.storage.getItem('user:' + request.params.id);

    if (!user) {
        sendError(response, 404, 'User not found');
        return;
    }

    response.setHeader('Content-Type', 'application/json');
    response.end(user);
});

CORS Headers

function setCorsHeaders(response) {
    response.setHeader('Access-Control-Allow-Origin', '*');
    response.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
    response.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');
}

app.options('/*', (request, response) => {
    setCorsHeaders(response);
    response.statusCode = 204;
    response.end();
});

app.get('/api/data', (request, response) => {
    setCorsHeaders(response);
    response.setHeader('Content-Type', 'application/json');
    response.end(JSON.stringify({ data: 'value' }));
});

---

Related

• request: Incoming request object
• context.http: HTTP client API
• context.storage: Persistent storage API
• context.info: Node metadata and environment