ng-postcode-js

JavaScript and TypeScript library for Nigeria's National Digital Alphanumeric Postcode System (NDAPS), the building-level postcode NIPOST launched in October 2026. Parse, validate and format postcodes offline, and call the postcode.gov.ng API for lookup, autocomplete and reverse geocoding.

Part of the ng-postcode project, which has the same behaviour in Rust, Python and Java and an MCP server for AI assistants. All four run the same shared test cases.

npm install ng-postcode-js

No runtime dependencies. Needs Node 22.12 or later, or any runtime with fetch. It is an ES module that require() can also load; a TypeScript project compiled to CommonJS needs "module": "nodenext" for that, as node16 rejects it.

Offline

Expected failures are returned as values, so the type checker makes you handle them.

import { Postcode, parse } from "ng-postcode-js";

const code = parse("ek 01 a03 fk 01");
if (code instanceof Postcode) {
  console.log(String(code)); // EK-01-A03-FK-01
  console.log(code.compact); // EK01A03FK01, store this
  console.log(code.spaced); // EK 01 A03 FK 01
  console.log(code.prefix("area")); // EK-01-A03-FK
} else {
  console.log(String(code)); // e.g. "invalid lga segment"
}

• parse accepts hyphenated, spaced or compact input in either case.
• parseLenient first swaps look-alikes that cannot occur where they stand (O/0, I/1, S/5, B/8) and reports how many it changed.
• fromSegments assembles a code from its parts and zero-fills the LGA and unit.
• parsePrefix reads a code cut off after a segment, such as the district EK-01-A03, and truncate cuts a code down to one. A prefix knows which codes it contains, so it groups them by state, LGA, district, or area.
• isValid answers yes or no.

A well-formed code is not necessarily assigned to a building. Only the API can confirm that a postcode exists.

API

import { Postcode, parse } from "ng-postcode-js";
import { ApiError, lookup } from "ng-postcode-js/api";
import { Client, TransportError } from "ng-postcode-js/client";

const code = parse("FC-03-B06-AG-12");
if (!(code instanceof Postcode)) throw new Error(String(code));

const client = new Client(process.env.NG_POSTCODE_API_KEY ?? "");
const found = await client.send(lookup(code, 1));

if (found instanceof ApiError || found instanceof TransportError) {
  console.error(String(found)); // e.g. "invalid_api_key (401): ..."
} else {
  console.log(found.valid, found.status); // true valid
}

ng-postcode-js/api covers lookup, autocomplete, reverse and nearby. Each returns a plain Request, and decode turns a status and body into a typed result, so it works with any HTTP client. A request that cannot succeed, such as a level outside 1 to 5, an empty autocomplete or a coordinate that is not finite, throws RangeError before anything is sent.

The client refuses redirects and a plain http base URL (except on this machine), so the key is never sent to another host or unencrypted. Response fields keep the API's own names, such as administrative_address.

Get a key from the NIPOST developer dashboard. Level 1 lookups confirm a code is assigned; levels 2 and up return address details and consume credits.

License

MIT