NodeJS Eval

Evaluate arbitrary JavaScript from Python, using a NodeJS sidecar process.

This combines:

• The Python nodejs-bin project, which bundles NodeJS (with npm and npx) into a PyPI package, and
• The JavaScript/TypeScript http-eval project, which runs a JavaScript evaluation server on a Unix domain socket.

---

Table of Contents

• Installation
• License
• Usage instructions

Installation

pip install nodejs-eval

License

nodejs-eval is distributed under the terms of the MIT license.

Usage instructions

Basic synchronous call

JavaScript code is evaluated as a function body within a synchronous or asynchronous JavaScript function, within an ECMAScript module.

Note that the NodeJS evaluator always only supports async mode on the Python side. However, the supplied JavaScript code can be either sync or async.

    from nodejs_eval import evaluator

    async with evaluator() as e:
        result = await e.run("return 6*7;")
        assert result == 42

Basic asynchronous call

    from nodejs_eval import evaluator

    async with evaluator() as e:
        result = await e.run_async(
            """
await new Promise(r => setTimeout(r, 2000));
return 6*7;
""")
        assert result == 42

Storing state on this

Evaluations run with a consistent JavaScript this context, so state can be stored on it:

    from nodejs_eval import evaluator

    async with evaluator() as e:
        await e.run("this.x = 6*7;")
        result = await e.run("return this.x;")
        assert result == 42

Import using dynamic await import()

Because code is executed within an ECMAScript module, you can use the dynamic async import() to import other modules.

This is easiest done in async mode:

    from nodejs_eval import evaluator

    async with evaluator() as e:
        result = await e.run_async(
            """
const os = await import("os");
return os.cpus();
"""
        )
        assert len(result) > 0