JSON.parse w/o blocking main thread

background-json-parse.js

'use strict';

const ivm = require('isolated-vm');

function handleParseJob(code) {
  return new ivm.ExternalCopy(JSON.parse(code), { transferOut: true });
}

function transferInExternalCopy(copy) {
  return copy.copy({ transferIn: true });
}

function buildParseFunction(parseRef) {
  return function parseJSONInBackground(json) {
    return parseRef.apply(undefined, [json])
      .then(transferInExternalCopy);
  }
}

async function main() {
  const isolate = new ivm.Isolate();
  const context = await isolate.createContext();
  context.globalReference().setSync('ivm', ivm);
  const script = await isolate.compileScript(`${handleParseJob}`);
  await script.run(context);

  const parseRef = await context.globalReference().get(handleParseJob.name);
  const parse = buildParseFunction(parseRef);

  console.time('all parse');
  await Promise.all([
    parse('{}'),
    parse('{"ok":true}'),
  ]).then(console.log, console.error);
  console.timeEnd('all parse');
}

main()
  .catch(console.error);