lnurl-pay.me/src/ecies.js

const receiverPublicKey = "02d38170b929dc26be2192071756edd5fb94c4e0cf1aec352ce4c8245e635d9bed";

import {hkdf} from "@noble/hashes/hkdf";
import {sha256} from "@noble/hashes/sha256";
import * as jscrypto from "jscrypto";
import * as secp from "@noble/secp256k1";
import { bech32 } from 'bech32';

let receiverPoint;

function getReceiverPoint() {
  if (receiverPoint)
    return receiverPoint;
  receiverPoint = secp.Point.fromHex(receiverPublicKey);
  return receiverPoint;
}

const noIV = jscrypto.Hex.parse("00000000000000000000000000000000");

export function ecEncrypt(plainText) {
  const pub = getReceiverPoint();
  const iv = noIV;
  const ek = secp.utils.randomPrivateKey();
  const epk = secp.Point.fromPrivateKey(ek);
  const sharedSecret = secp.getSharedSecret(ek, pub);
  const key = hkdf(sha256,new Uint8Array([...epk.toRawBytes(),...sharedSecret]));
  const jskkey = new jscrypto.Word32Array(key);

  const ed = jscrypto.AES.encrypt(jscrypto.Utf8.parse(plainText),
				  jskkey,{mode:jscrypto.mode.GCM, padding:jscrypto.pad.NoPadding, iv: noIV});
  const at = jscrypto.mode.GCM.mac(jscrypto.AES,jskkey,noIV,null,ed.cipherText,16);

  const ctbytes = new Uint8Array([...at.toUint8Array(),
				  ...epk.toRawBytes(true),
				  ...ed.cipherText.toUint8Array()]);
  const bech = bech32.encode("",bech32.toWords(ctbytes), 1024);
  return bech.slice(1,-6)
}