pypi i 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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Installing the reference interpreter

pip install dnjs
dnjs --help


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 ? "" : ""

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": ""
    "name": "account",
    "ip": ""

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

def some_route():
    return render("commentsPage.dn.js", comments)

And the endpoint will return:

        <script src="someScript.js">
                Comment 0 says: hiya!
                Comment 1 says: oioi

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"},


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

As a jq replacement

JSON='[{foo: 1, bar: "one"}, {foo: 2, bar: "two"}]'
echo $JSON | dnjs - -p 'a=>a.map(b=>[b.bar, b.foo])'
[["one", 1], ["two", 2]]


echo $JSON | dnjs - -p 'a=>a.map(b=>[b.bar, b.foo])' --csv

csv, raw

echo $JSON | dnjs - -p 'a=>a.map(b=>[b.bar, b.foo])' --csv --raw


(While dnjs is implemented in python, this is very slow).

JSON='{foo: 1, bar: "one"}\n{foo: 2, bar: "two"}'
echo $JSON | while read l; do echo $l | dnjs - -p 'a=>a.bar' --raw; done


Remember, you can flatten arrays with:

.reduce((a, b)=>[...a, ...b], [])

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:

  • 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. Brackets are not required for one argument, functions are called with the number of arguments provided.
  • Ternary expressions, only in the form a === b ? c : d. Equality should be implemented however JavaScript does.
  • Map, filter, reduce, map over dict, dict from entries, in the form a.map((v, i) => b), a.filter((v, i) => b), a.reduce((x, y) => [...x, ...y], []), 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.


Originally the name stood for DOM Notation JavaScript.



These functions return JSON-able data:

from dnjs import get_default_export, get_named_export

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!


Install dev requirements with:

pip install -r requirements-dev.txt

Run tests with:


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/*


Javascript validation library to follow - see TODO section below.

Run tests with:

npm install
npm test


  • 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.
  • 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? Specify PATHs that it's permitted to import from.
  • 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.

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