GPS.js

GPS.js is a typed NMEA 0183 parser for GPS and GNSS receivers. It parses individual sentences, consumes arbitrarily split streams, emits sentence-specific events, and maintains a normalized receiver state.

The library handles supplied NMEA text only. Opening serial devices, sockets, and other transports remains an application concern.

Project page: raw.org/software/libraries/gps-js

Installation

GPS.js 0.9 requires Node.js 20 or newer.

npm install gps

Quick Start

import GPS from 'gps';

const gps = new GPS();

gps.on('GGA', fix => {
  console.log(fix.lat, fix.lon, fix.alt);
});

gps.update(
  '$GPGGA,224900.000,4832.3762,N,00903.5393,E,1,04,7.8,498.6,M,48.0,M,,0000*5E'
);

CommonJS is supported as well:

const GPS = require('gps');
const gps = new GPS();

The package includes TypeScript declarations. Event names narrow callback payloads automatically:

import GPS from 'gps';

const gps = new GPS();

gps.on('RMC', record => {
  record.speed;     // number | null, in km/h
  record.navStatus; // safe | caution | unsafe | not valid | null
});

Parsing Sentences

Use GPS.Parse() when accumulated receiver state and events are unnecessary:

import GPS from 'gps';

const sentence = '$GPGGA,224900.000,4832.3762,N,00903.5393,E,1,04,7.8,498.6,M,48.0,M,,0000*5E';
const fix = GPS.Parse(sentence);

if (fix && fix.valid && fix.type === 'GGA') {
  console.log(fix.lat, fix.lon, fix.alt);
}

GPS.Parse() returns false for unsupported or structurally rejected input. A recognized sentence with a bad checksum is returned with valid: false.

gps.update() emits recognized checksum-invalid records so applications can inspect reception errors, but does not merge them into gps.state or multipart TXT buffers. Both rejected and checksum-invalid input increment state.errors.

Streaming Input

updatePartial() buffers incomplete chunks and accepts CRLF or LF delimiters:

const gps = new GPS();

gps.on('data', record => console.log(record));

gps.updatePartial('$GPGGA,224900.000,4832.3762,N,');
gps.updatePartial('00903.5393,E,1,04,7.8,498.6,M,48.0,M,,0000*5E\r\n');

Events

Subscribe to data for every parsed sentence or use a sentence identifier such as GGA, RMC, or GSV:

const onFix = fix => console.log(fix);

gps.on('GGA', onFix);
gps.off('GGA', onFix);
gps.off('GGA'); // Remove every GGA listener.

on() and off() return the receiver instance for chaining.

Receiver State

gps.state is updated in place as valid sentences arrive. It includes counters and the latest available navigation values:

gps.on('data', record => {
  if (record.valid) {
    console.log(gps.state.lat, gps.state.lon, gps.state.speed);
  }
});

Depending on the received sentences, state may contain time, lat, lon, alt, speed, track, heading, fix, dilution values, active satellite IDs, and visible satellite records. Snapshot values when historical states are needed.

Supported Sentences

Sentence	Data
GGA	Fix position, quality, altitude, and dilution
GSA	Fix mode, active satellites, dilution, and GNSS system
RMC	Position, speed, track, date, mode, and navigation status
VTG	True/magnetic track and speed
GSV	Satellites in view, signal strength, and GNSS system
GLL	Geographic position and status
ZDA	UTC date/time and local offset
GST	Position error statistics
HDT	Heading relative to true north
GRS	Range residuals
GBS	Satellite fault detection data
GNS	Multi-constellation fix data
TXT	Single-part and multipart receiver text

GPS, GLONASS, Galileo, BeiDou, QZSS, and NavIC identifiers are normalized where the sentence provides enough information.

Every parsed record includes:

• type: the sentence identifier
• raw: the original sentence
• valid: whether the checksum matches

Blank optional numeric fields are represented as null rather than NaN.

Geospatial Helpers

Coordinates use decimal degrees. Distances are returned in kilometers and headings use compass degrees, with north at 0 and east at 90.

const distance = GPS.Distance(48.8566, 2.3522, 51.5074, -0.1278);
const heading = GPS.Heading(48.8566, 2.3522, 51.5074, -0.1278);

const routeLength = GPS.TotalDistance([
  { lat: 48.8566, lon: 2.3522 },
  { lat: 50.1109, lon: 8.6821 },
  { lat: 51.5074, lon: -0.1278 }
]);

Distance() uses the haversine formula on a spherical Earth model. It is suitable for navigation estimates, not survey-grade ellipsoidal geodesy.

Browser Usage

The browser IIFE exposes a global GPS constructor and also supports AMD loaders:

<script src="https://unpkg.com/gps/dist/gps.min.js"></script>
<script>
  const gps = new GPS();
</script>

The browser ESM build is available through the gps/browser package export:

import GPS from 'gps/browser';

Published artifacts are:

• dist/gps.js: CommonJS
• dist/gps.mjs: ES module
• dist/gps.min.js: minified browser IIFE with AMD support
• dist/gps.min.mjs: minified browser ES module

Development

npm install
npm test

npm test runs strict TypeScript checking, builds every distribution, validates CommonJS and ESM type consumers, and executes the runtime and distribution suites.

License

Copyright (c) 2026 Robert Eisele

Licensed under the MIT License.