Function: buildMessage()

buildMessage(init): Hl7Message

Construct an outbound Hl7Message from semantic MSH fields (SER-06). Synthesises a complete MSH RawSegment per D-10/D-11 and hands to new Hl7Message({...}). Callers chain .addSegment(name, fields) (mutation method) to append PID, OBX, etc.

Defaults applied when fields are omitted (D-10):

• controlId → generateControlId() (D-12)
• timestamp → formatHl7Timestamp(new Date()) (D-13)
• version → "2.5"
• processingId → "P"
• sendingApp/sendingFacility/receivingApp/receivingFacility → empty

Encoding characters are always DEFAULT_ENCODING_CHARACTERS (D-14); no option to customise in v1.

Empty string vs. omitted field (W1): at the HL7 wire level, passing sendingApp: "" and omitting sendingApp produce IDENTICAL output (both emit as absent: || at the MSH-3 position). If you need to emit an HL7 explicit null ("", the two-char literal) at a specific position, build the message first, then use setField:

const msg = buildMessage({ type: "ADT^A01" });
msg.setField("MSH.3", '""');  // sets RawField.isNull = true
// msg.toString() now emits MSH-3 as `""` (2 chars), not as absent.

BuildMessageInit carries the same note on the input shape.

Parameters

init

BuildMessageInit

Returns

Hl7Message

Example

import { buildMessage, parseHL7 } from "@cosyte/hl7";
const msg = buildMessage({
  type: "ADT^A01",
  sendingApp: "CLINIC",
  sendingFacility: "MAIN",
  receivingApp: "LAB",
  receivingFacility: "REF",
}).addSegment("PID", ["", "", "MRN123", "", "Doe^John"]);

// Spec-clean HL7 string round-trips through parseHL7:
const round = parseHL7(msg.toString());
console.log(round.meta.type); // "ADT^A01"