nix-eval

Evaluate Nix code on the browser with Tvix and WebAssembly.

Installation

npm install nix-eval

Usage

Create an evaluator once, then use it to evaluate Nix source. The evaluator initializes its WebAssembly module on first use.

import { createEvaluator } from "nix-eval";

const evaluator = await createEvaluator({ strict: true });
const result = await evaluator.eval("6 * 7");

console.log(result.output); // "42"

Pass { strict: true } to force the final value before rendering. This resolves lazy values in attribute sets and lists instead of displaying <CODE>.

Pass a location as the second argument to associate diagnostics with a source name. It defaults to "<string>".

const result = await evaluator.eval("1 / 0", "example.nix");
console.log(result.errors);

Acknowledgments

This package is based on Tvix and its Bolt playground, packaged for distribution as an npm library. It was also greatly inspired by Tour of Nix.