Escape decoder

Unified plugin to decode HL7v2 escape sequences in literal values.

What it does

Walks an HL7v2 AST and decodes escape sequences found in subcomponent nodes, replacing node.value with the decoded text. It handles the HL7 delimiter escapes (\F\, \S\, \R\, \T\, \E\), hexadecimal escapes (\Xdddd\), line-break directives (\.br\), and strips the highlighting markers (\H\, \N\). The original raw text is preserved on node.data.raw so the transformation is non-destructive.

Install

npm install @glion/decode-escapes

Use

import { hl7v2DecodeEscapes } from "@glion/decode-escapes";
import { hl7v2Parser } from "@glion/parser";
import { unified } from "unified";

const msg = `OBX|1|TX|ID123||Patient allergic to \\F\\Peanuts\\F\\ and \\.br\\Severe reaction`;

const file = await unified()
  .use(hl7v2Parser)
  .use(hl7v2DecodeEscapes)
  .process(msg);

Before decoding, subcomponent.value contains the raw HL7 text:

{
  "type": "subcomponent",
  "index": 1,
  "value": "Patient allergic to \\F\\Peanuts\\F\\ and \\.br\\Severe reaction"
}

After this plugin runs:

{
  "type": "subcomponent",
  "index": 1,
  "value": "Patient allergic to |Peanuts| and \rSevere reaction"
}

API

unified().use(hl7v2DecodeEscapes[, options])

Decode HL7v2 escape sequences in literal nodes.

Parameters

• options.delimiters (optional) — Override delimiters. If omitted, the plugin reads them from Root.data.delimiters (set by the parser). Defaults to the HL7 standard (| ^ ~ & \).

Returns

Nothing (undefined). Mutates the AST in-place.

Behavior

The plugin visits every subcomponent node and rewrites node.value. The original text is preserved on node.data.raw so downstream plugins can recover it.

Each escape sequence is decoded as follows:

Delimiter resolution order: Root.data.delimiters (preferred, set by the parser) → options.delimiters → HL7 defaults.

The plugin only transforms AST nodes and does not execute code. The inverse operation is provided by @glion/encode-escapes.