index.js

"use strict";
const express = require("express");
const util = require("util");
const exec = util.promisify(require("child_process").exec);
const app = express();

app.get("/", async (req, res) => {
  const wait_time = parseInt(req.query.wait) || 150;
  let state = false;
  cmd(wait_time, () => {
    state = true;
  });
  {
    let i=0;
    while(true){
      i++;
      await sleep(1);
      res.write(`wait ${i} seconds\n`);
      if (state){
        break;
      }
    }
  }
  res.end();
});

async function cmd(wait_time, callback){
  console.log(`wait_time: ${wait_time}`);
  const { stdout, stderr } = await exec(`sleep ${wait_time};echo ok`);
  console.log(`stdout: ${stdout}`);
  console.log(`stderr: ${stderr}`);
  callback();
}
function sleep(time){
  return new Promise((resolv,reject) => {
  setTimeout(() => {
    resolv();
  }, time * 1000);
  });
}

const port = process.env.PORT || 8080;
app.listen(port, () => {
  console.log("listening on port", port);
});