write

Writes content to the response body in a MARS Engine handler.

Syntax

write('key', 'text') // Writes a JSON response object {key: 'text'}
write(image); // If 'image' is a binary file writes the binary data with appropriate headers (eg. image/png, image/jpeg)
write('data', obj) // Serializes obj to JSON and returns it under the key 'data'

Details

The write function sets the response body for the current request.

• Accepts strings, objects or binary.
• If an object is passed, MARS Engine automatically serializes it to JSON and sets the Content-Type header to application/json.
• If binary data is passed, it is written directly with no transformation trying to set the appropriate Content-Type.
• Subsequent calls to write do not overwrite previous calls, they append if possible. Eg. You can't respond with two files in one response, so calling write twice leads to improper formatting.

Supported Types

Input Type	Behavior	Content-Type set
string	Sends JSON text under the key 'unset key'	application/json
Buffer	Sends raw binary data	As appropriate
object	Serializes to JSON	application/json

Examples

Plain text response

response.setContentType('text/plain')
write('Hello, world!')

JSON response

write({ message: 'Success', userId: 42 })

Binary response

const image = fs.read("path/to/image.png")
write(image.data)

Text response with suggested filename

const csvData = "John,Doe,1980\nMary,Jane,1990"
response.setContentType('text/csv')
response.header("Content-Disposition", 'attachment;filename="data_export.csv"');
write(csv)

Combined with status

response.status(201)
write({ status: 'created', id: 42 })

Notes

• You can use write() multiple times per request; it will append to any previous content if possible
• Pair with response.status() and header() for full response control.