Python-JavaScript

JavaScript-style objects, methods and functions for Python 3.14+, using the case-sensitive JavaScript namespace. An alpha compatibility layer with a documented subset of ECMAScript behavior.

python -m pip install Python-JavaScript==0.1.0

from JavaScript import Array, JSON, Math, Object, String, undefined

people = JSON.parse('[{"name":"Ada","score":8},{"name":"Lin","score":6}]')
names = people.filter(lambda person: person.score >= 7).map(
    lambda person: person.name.toUpperCase()
)
assert names.join(", ") == "ADA"

profile = Object({"name": String("Ada"), "scores": Array.of(8, 6)})
assert profile.missing is undefined
assert profile.scores.reduce(lambda total, score: total + score, 0) == 14
assert Math.round(2.5) == 3
assert JSON.stringify(profile) == '{"name":"Ada","scores":[8,6]}'

Explicit Object, Array, String and Number values expose JavaScript names and behavior. Ordinary Python literals and operators retain Python semantics. Objects and arrays compare by identity and remain truthy when empty. Use Boolean(value) or truthy(value) when testing JavaScript truthiness of values that might include Python containers.

Standalone packages

Installation includes two independently useful dependencies:

import asyncio
from fetch_api import fetch
from JavaScript import JSON

async def main():
    response = await fetch("https://example.com/api/people")
    if not response.ok:
        raise RuntimeError(f"HTTP {response.status}")
    people = JSON.parse(await response.text())
    return people

# Run against your own JSON endpoint:
# people = asyncio.run(main())

JavaScript.fetch, Promise, Headers, Request, Response and FetchError are the same objects exported by fetch_api. Fetch 0.2.0 changes the old from javascript import fetch spelling to from fetch_api import fetch.

response.json() retains Fetch's standalone JSONObject/list result. Use JavaScript.JSON.parse(await response.text()) for runtime Object/Array/String values. Standalone import JSON preserves Python integers and containers; from JavaScript import JSON uses binary64 numbers and JavaScript serialization rules for its supported subset.

Supported surface

Core data objects and sparse arrays; UTF-16 String methods; Number predicates and prefix parsers; Boolean conversion; selected Math functions; JSON; and the standalone Fetch/Promise APIs. See the complete compatibility matrix for method lists and limits.

Python keywords require Array.from_, Object.is_, and Promise.finally_. None represents null; undefined is a separate singleton. Array bracket indices follow JavaScript rules: values[-1] is a named property, and values.at(-1) accesses the last element. Array(3) creates three holes; Array.of(3) creates one element containing 3.

The longer-term goal is a binding-aware Python-to-JavaScript translator. v0.1.0 provides the runtime foundation; it does not translate source or execute JavaScript. Prototypes, descriptors, Date, RegExp, Map/Set, typed arrays, browser globals and other unlisted APIs remain future work. Development is tracked in the issues and Project.

Development

uv sync
uv run python -m unittest discover -s tests -v
uv build

Node.js 24 runs the native ECMAScript differential fixture. That test is skipped when Node is absent locally; CI and release builds require it. Runtime code needs only Python and the two declared companions. Tests make no external network requests.