RPC between Browser and Node.js

rpc-client.js

async function exec(name, ...args) {
  const res = await fetch(`/rpc/${name}`, {
    method: "POST",
    headers: {
      "content-type": "application/json"
    },
    body: JSON.stringify(args)
  });
  const json = await res.json();
  return json;
}

rpc-server.js

const express = require("express");

module.exports.start = function(options) {
  const { port, public, funcs } = options;
  const functions = new Map();
  for (const name in funcs) {
    functions.set(name, funcs[name]);
  }
  const app = express();
  app.use(express.static(public));
  app.use(express.json());
  app.post("/rpc/:name", (req, res) => {
    const funcName = req.params.name;
    if (functions.has(funcName)) {
      (async () => {
        try {
          const args = req.body;
          const ret = await functions.get(funcName).apply(null, args);
          res.send(ret);
        } catch (e) {
          console.log(e);
          res.status(500).send({ message: e.message });
        }
      })();
    } else {
      res.status(404).send();
    }
  });
  return new Promise((resolve, reject) => {
    const server = app.listen(port, e => {
      if (e) {
        reject(e);
      } else {
        resolve(server);
      }
    });
  });
};