Static server.js example for ES module

server.js

// Settings
const appRoot = "";
const srcRoot = "src";
const staticRoot = "statics";


const path = require('path');
const Koa = require('koa');
const send = require('koa-send');

const srcAbsPath = path.resolve(__dirname, srcRoot);
const staticAbsPath = path.resolve(__dirname, staticRoot);
const nodeModulesRoot = path.resolve(__dirname, 'node_modules');


async function sendFile(ctx, pt) {
  if (pt.startsWith("~")) {
    // node_modules
    return await send(ctx, pt.substr(1), { root: nodeModulesRoot });
  } else if (pt.startsWith(`${appRoot}/${srcRoot}/`)) {
    // src
    pt = pt.substr(srcRoot.length + 1);
    if (!path.extname(pt)) pt += '.js';
    return await send(ctx, pt, { root: srcAbsPath });
  } else {
    // static
    return await send(ctx, pt, { root: staticAbsPath, index: 'index.html' });
  }
}


function createServer() {
  const app = new Koa();

  app.use(async (ctx, next) => {
    await next();

    // Set cors headers
    ctx.set('Access-Control-Allow-Origin', '*');
    ctx.set('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
    ctx.set('Access-Control-Allow-Headers', 'Content-Type');
  });

  app.use(async (ctx, next) => {
    if (!['GET', 'HEAD'].includes(ctx.method)) {
      ctx.status = 405;
      ctx.body = "Method now allowed";
      return;
    }

    let pt = ctx.path;
    let done = false;
    if (pt.startsWith(appRoot)) {
      pt = pt.substr(appRoot.length);

      try {
        if (pt.startsWith('/~')) {
          done = await send(ctx, pt.substr(2), { root: nodeModulesRoot });
        } else {
          done = await sendFile(ctx, pt);
        }
      } catch(err) {
        if (err.status !== 404) throw err;
      }
    } else {
      ctx.status = 404;
      ctx.body = "Not found";
      return;
    }
    if (!done) await next();
  });

  return app;
}

createServer().listen(process.env.PORT || 3000);