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README.md

dnjs

dnjs is a pure subset of JavaScript that wants to replace (across many host languages):

  • overly limiting/baroque configuration languages
  • mucky string based html/xml templating

It is powerful yet familiar, and the reduced syntax makes it easy to implement (the reference implementation in Python took a couple of days to write) and easy to reason about. Currently the state is very alpha - see the TODO at the end.

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║ ╔═══════════════╗            ║
║ ║ ╔══════╗      ║            ║
║ ║ ║ JSON ║ dnjs ║ JavaScript ║
║ ║ ╚══════╝      ║            ║
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An article on using dnjs: evolving backend → frontend rendered Python/JS apps with dnjs

Installing the reference interpreter

pip install dnjs
dnjs --help

Examples

Some of these examples reference other files in the examples folder.

For configuration:

import { environments } from "./global.dn.js"

// names of the services to deploy
const serviceNames = ["signup", "account"]

const makeService = (environment, serviceName) => ({
    name: serviceName,
    ip: environment === environments.PROD ? "189.34.0.4" : "127.0.0.1"
})

export default (environment) => serviceNames.map(
    (v, i) => makeService(environment, v)
)

Let's use the reference implementation written in Python to run these (this also has a Python API documented below):

dnjs examples/configuration.dn.js examples/environment.json | jq

Gives us:

[
  {
    "name": "signup",
    "ip": "127.0.0.1"
  },
  {
    "name": "account",
    "ip": "127.0.0.1"
  }
]

For html templating

dnjs prescribes functions for making html, that handily are a subset of mithril (this makes it possible to write powerful, reusable cross-language html components).

Given the file commentsPage.dn.js:

import m from "mithril"

import { page } from "./basePage.dn.js"

const commentList = (comments) => m("ul",
    comments.map((comment, i) => m("li", `Comment ${i} says: ${comment.text}`))
)

export default (comments) => page(commentList(comments))

Then in a python webserver we can render the file as html:

from dnjs import render

@app.route("/some-route"):
def some_route():
    ...
    return render("commentsPage.dn.js", comments)

And the endpoint will return:

<html>
    <head>
        <script src="someScript.js">
        </script>
    </head>
    <body>
        <ul>
            <li>
                Comment 0 says: hiya!
            </li>
            <li>
                Comment 1 says: oioi
            </li>
        </ul>
    </body>
</html>

Or we can use the same components on the frontend with mithril:

import page from "../commentsPage.dn.js"
...
m.mount(document.body, page)

Or we can render the html on the command line similar to before:

dnjs examples/commentsPage.dn.js examples/comments.json --html

Note, that without the --html flag, we still make the following JSON, the conversion to html is a post-processing stage:

{
  "tag": "html",
  "attrs": {
    "className": ""
  },
  "children": [
    {
      "tag": "head",
      "attrs": {
...

For css templating

Using --css will post-process eg:

export default {
  ".bold": {"font-weight": "bold"},
  ".red": {"color": "red"},
}

to:

.bold {
    font-weight: bold;
}
.red {
    color: red;
}

How exactly does dnjs extend JSON?

Remember dnjs is a restriction of JavaScript, the aim is not to implement all of it, any more than JSON is.

Here are all the extensions to JSON, the grammar can be found here.

  • Comments with //.
  • Optional trailing commas.
  • Unquoted keys in objects.
  • import { c } from "./b.dn.js", import b from "./b.dn.js". Non-local imports are simply ignored (so as to allow importing m as anything).
  • export default a, export const b = c.
  • dicts and lists can be splatted with rest syntax: {...a}/[...a].
  • Functions can be defined with const f = (a, b) => c syntax.
  • Ternary expressions, only in the form a === b ? c : d. Equality should be implemented however JavaScript does.
  • Map, filter, map over dict, dict from entries, in the form a.map((v, i) => b), a.filter((v, i) => b), Object.entries(a).map(([k, v], i) => b), Object.fromEntries(a).
  • Hyperscript, somewhat compatible with mithril - m("sometag#some-id.some-class.other-class", {"href": "foo.js", "class": ["another-class"]}, children), this evaluates to dicts like {"tag": "sometag", "attrs": {"id": "some-id", className: "some-class other-class another-class", "href": "foo.js", "children": children}. m.trust(a) to not escape html.
  • Multiline templates in the form `foo ${a}`, dedent(`foo ${a}`). dedent should work the same as this npm package.
  • Lists have .length, .includes(a) attributes.

Name

Originally the name stood for DOM Notation JavaScript.

Python

API

These functions return JSON-able data:

from dnjs import get_default_export, get_named_export

get_default_export(path)
get_named_export(path, name)

This function returns html as a str:

from dnjs import render

render(path, *values)

The types used throughout dnjs are fairly simple dataclasss , there's not much funny stuff going on in the code - check it out!

Development

Install dev requirements with:

pip install -r requirements-dev.txt

Run tests with:

pytest

Pin requirements with:

pip-compile -q; cat requirements.in requirements-dev.in | pip-compile -q --output-file=requirements-dev.txt -

Rebuild and publish (after upversioning) with:

# up version setup.py
rm dist/*; python setup.py sdist bdist_wheel; twine upload dist/*

JS

Javascript validation library to follow - see TODO section below.

Run tests with:

npm install
npm test

TODO

  • Use on something real to iron out bugs.
  • Spec out weird behaviour + make the same as js:
    • numbers
    • ===
  • Nicer docs:
    • Write up why we don't need filters like | to_human.
  • Consider onclick, onkeydown, on... functions... and how we want to handle them / attach them on reaching the browser in a isomophic setup.
  • Decide what else should be added:
    • Common string functions like upper case, replace etc?
    • parseInt etc..
  • Standalone (in c/rust/go? with Python bindings) to JSON program.
  • Name things in the grammar, catch lark exceptions and make custom user ones.
  • Write JS library that simply wraps mithril render and has a dnjs.isValid(path) function that uses the grammar (doing this may involve removing some lark-specific bits in the grammar.
  • Typescript support?
  • Consider what prevents dnjs from becoming a data interchange format - eg. infinite recursion. --safe mode should probably have no functions and no imports.
  • Allow importing JSON using Experimental JSON modules](https://nodejs.org/api/esm.html#esm_experimental_json_modules).
  • Remove accidental non-js compatability - eg. template grammar is a bit wacky.
  • Handle _ambig

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