The express module exposes a small Express-style route registration API for Goja-hosted applications. It is intentionally Express-style, not full Express-compatible: it supports route handlers and static mounts, but not middleware stacks, routers, next(), template engines, or npm Express plugins.

Go setup

express is runtime-scoped because it needs a configured gojahttp.Host and runtime owner. Install it with modules/express.NewRegistrar(host) rather than through the default native module registry.

host := gojahttp.NewHost(gojahttp.HostOptions{
    Dev:      true,
    Renderer: uidsl.RenderAny,
})

factory, err := engine.NewRuntimeFactoryBuilder().
    WithModules(
        express.NewRegistrar(host),
        uidsl.NewRegistrar(),
    ).
    Build()

pkg/gojahttp owns the reusable HTTP host, route matching, request/response DTOs, body parsing, sessions, static mounts, and dispatch into the Goja runtime. The host is renderer-neutral; HostOptions.Renderer decides how res.html(value) renders non-string values.

JavaScript usage

const express = require("express");
const ui = require("ui.dsl");

const app = express.app();

app.get("/hello/:name", (req, res) => {
  return ui.page(
    { title: "Hello" },
    ui.h1("Hello " + req.params.name)
  );
});

app.post("/api/echo", (req, res) => {
  res.status(201).json({ body: req.body });
});

Handlers may call res.* explicitly. If a handler returns a string, the host sends it as text/HTML depending on content. If a handler returns any other non-null value, the host calls res.html(value) and uses the configured renderer.

App API

app.get(pattern, handler)
app.post(pattern, handler)
app.put(pattern, handler)
app.patch(pattern, handler)
app.delete(pattern, handler)
app.all(pattern, handler)
app.static(prefix, directory)
app.staticFromAssetsModule(prefix, assetsModule, root)

app.static(prefix, directory) serves a real host filesystem directory.

app.staticFromAssetsModule(prefix, assetsModule, root) serves files directly from a read-only embedded fs module, for example:

const express = require("express");
const assets = require("fs:assets");
const app = express.app();

app.staticFromAssetsModule("/static", assets, "/app/public");

Route patterns support exact paths, :params, and * wildcards.

Request object

Handlers receive a plain JavaScript request object:

type Request = {
  method: string;
  url: string;
  path: string;
  query: Record<string, string | string[]>;
  params: Record<string, string>;
  headers: Record<string, string>;
  cookies: Record<string, string>;
  session: { id: string; isNew: boolean; cookieName: string } | null;
  ip: string;
  body: unknown;
  rawBody: string;
};

JSON and form bodies are parsed automatically. Other request bodies are exposed as strings.

Response object

res.status(code)
res.set(name, value)
res.type(contentType)
res.json(value)
res.send(value)
res.html(value)
res.redirect(url)
res.redirect(status, url)
res.end()

res.html(value) requires a renderer in gojahttp.HostOptions. With modules/uidsl.RenderAny, route handlers can return or send ui.dsl nodes directly.