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http://hop.inria.fr Hop.js: a multitier JavaScript

Hop.js (aka Hop) is:

  • A multitier JavaScript:
    • a single code runs on the client and the server.
  • A compliant JavaScript implementation:
    • EcmaScript 5.1 compliant;
    • EcmaScript 6 features (modules, async/await, proxy objects, ...);
    • Nodejs compatibility.
  • An extended JavaScript:
    • builtin HTML: native HTML syntax support and multitier dom.
    • server-side web workers.
    • websockets.
  • Two implementations:
    1. A Nodejs embedding (i.e., Hop.js can be installed inside Nodejs via an NPM package).
    2. A builtin multi-threaded web server.

Note

Hop.js also supports the Scheme programming language. When using the nativer Hop.js version (as opposed to the Nodejs hostsed version), JavaScript and Scheme are fully interoperable and applications can mix both languages. This page mostly describes the JavaScript layer. The Scheme layer is described in a dedicated programming manual.

Hop.js programs execute in the context of a builtin web server. They define services, which are super JavaScript functions that get automatically invoked when HTTP requests are received. As service associates an URL to a JavaScript and enables calls by the means of HTTP requests:

// hello.hop.mjs
import { Hop } from "@hop/hop";

const hop = new Hop({ports: {http: 8888}});

function hello(o) {
  return "hello world";
}

const Hello = hop.Service(hello);
hop.listen().then(() => console.log(`${Hello()} ready...`);

To run this program put this code in the file hello.hop.mjs, compile it

$ hopc.mjs hello.hop.mjs -o hello.mjs

and execute it:

$ nodejs hello.mjs

You can now browse http://localhost:8888/hello.

Hop.js extends JavaScript with the geniune HTML language. if we want to modify our service to make it returns an HTML document, we can use:

function hello() {
  return <html><div>hello world</div></html>;
}

Hop.js is multitier. That is client-side codes are also implemented in Hop. The ~{ mark switches from server-side context to client-side context:

function hello() {
  return <html><div onclick=~{alert("world")}>hello</div></html>;
}

Hop.js client-side code and server-side can also be mixed using the \${ mark:

service hello({ name: who }) {
  return <html><div onclick=~{alert("Hi " + ${who} + "!")}>hello</div></html>;
}

By default Hop.js only accepts to serve authenticated requests. Users must be declared when instantiating the server. The following declares two users. First, a user named hopjs whose password is abcdef, and that is allowed to execute any Hop.js service (the declaration services: "\*") and download any file readable from the server process (the declaration directories: "\*"). Second, the "anonymous" user, which is associated to unauthenticated requests. No password is associated with that user. He is only allowed to run a wizard service and is only allowed to access the Hop.js runtime files.

import { Hop } from "@hop/hop";

const users = [ {
      name: "hopjs",
      password: Hop.passwordEncrypt("hopjs", "abcdef"), // should be precomputed with "hopuser.mjs"
      services: "*",
      directories: "*"
   }, { 
      name: "anonymous",
      services: ["wizard"],
      directories: hop.loadPath
   } ];
   
const hop = new Hop({ports: {http: 8888}, users});

Caution

Of course, passwords should not be included as plain texts in programs. Instead they should be precomputed and only the result of the encryption should be included in the program. The Hop.js distribution provided the bin/hopuser.mjs that generates user declarations with an encrypted password.

You are now ready to execute Hop.js programs! Many more additional examples can be found in the source development tree.

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