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sass compileString with in-memory importer: working versions (tested 2026-10-16)

Compile Sass from a string with dart-sass, using variables and mixins from an in-memory @use module provided by a custom canonicalize/load importer, compressed output, and an undefined-variable error assertion, all offline.

passed3 passed · 0 failed2026-10-16 00:54 UTC
Status
passed
Last passed
2026-10-16 00:54 UTC
Tests
3 / 3
Language
TypeScript
Runtime
node v22.23.3
pinned versions3
sass@1.105.1@types/node@26.6.5tsx@4.23.15
run it
npm install --no-audit --no-fund --ignore-scripts=false
npm test
test environment
node v22.23.3
linux 6.17.0-1022-azure
x64
runner: github-actions 38831610868

The code

Exactly the files that passed. Your agent can pull them with get_recipe("sass-compile-string-importer") (install), or see them on GitHub.

package.json
{
  "name": "sass-compile-string-importer",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node --import tsx --test test/*.test.ts"
  },
  "dependencies": {
    "sass": "1.105.1"
  },
  "devDependencies": {
    "@types/node": "26.6.5",
    "tsx": "4.23.15"
  }
}
src/compiler.ts
import * as sass from "sass";

export function createMemoryImporter(
  modules: Record<string, string>,
): sass.Importer<"sync"> {
  return {
    canonicalize(url: string): URL | null {
      return Object.prototype.hasOwnProperty.call(modules, url)
        ? new URL(`memory:${url}`)
        : null;
    },
    load(canonicalUrl: URL): sass.ImporterResult | null {
      const contents = modules[canonicalUrl.pathname];
      if (contents === undefined) return null;
      return { contents, syntax: "scss" };
    },
  };
}

export function compileWithModules(
  source: string,
  modules: Record<string, string>,
): string {
  const result = sass.compileString(source, {
    importers: [createMemoryImporter(modules)],
    style: "compressed",
  });
  return result.css;
}
test/compiler.test.ts
import { test } from "node:test";
import assert from "node:assert/strict";
import { compileWithModules, createMemoryImporter } from "../src/compiler.ts";

const theme = `
$primary: #336699;
$radius: 4px;

@mixin rounded($r: $radius) {
  border-radius: $r;
}
`;

test("compiles variables and mixins from an in-memory @use module", () => {
  const css = compileWithModules(
    `@use "theme";
     .button {
       color: theme.$primary;
       @include theme.rounded(8px);
     }`,
    { theme },
  );
  assert.equal(css.trim(), ".button{color:#369;border-radius:8px}");
});

test("throws on an undefined variable", () => {
  assert.throws(
    () =>
      compileWithModules(
        `@use "theme";
         .bad { color: theme.$missing; }`,
        { theme: "$primary: #336699;" },
      ),
    /Undefined variable/,
  );
});

test("canonicalize resolves known modules and rejects unknown ones", () => {
  const importer = createMemoryImporter({ theme: "$primary: red;" });
  const canonical = importer.canonicalize("theme", {} as sass.CanonicalizeContext);
  assert.equal(canonical?.pathname, "theme");
  assert.equal(importer.canonicalize("nope", {} as sass.CanonicalizeContext), null);
});

Connect to ProvenPin

Add the free MCP server so your agent can pull this recipe and others like it. Same setup as the docs.

terminal
claude mcp add --transport http provenpin https://mcp.provenpin.com/mcp

Any other MCP client: Streamable HTTP at https://mcp.provenpin.com/mcp. No API key, no signup.