From JSON-LD to TriG, requires "jsonld" and "n3" npm packages.

json-ld.js

import * as jsonld from "jsonld";
import * as n3 from "n3";

const doc = { "YOUR" : "JSONLD" };

const nquads = await jsonld.toRDF(doc, { format: "application/n-quads" });
const parser = new n3.Parser({ format: "application/n-quads" });
const writer = new n3.Writer({ format: "application/trig" });

await parser.parse(nquads, (error, quad, prefixes) => {
  if (error) console.log(`PARSE ERROR: ${error}`);
  if (quad) writer.addQuad(quad);
});

await writer.end((error, result) => {
  if (error) console.log(`WRITE ERROR: ${error}`);
  console.log(result);
});

There must be a way to not write nquads first but since jsonld and n3 use different underlying representation of quads, going through plaintext is the quick and dirty way.