bundle.test.mjs

import assert from 'node:assert/strict';
import { readFile } from 'node:fs/promises';
import { dirname, join } from 'node:path';
import { fileURLToPath } from 'node:url';
import { describe, it } from 'node:test';
import vm from 'node:vm';

const here = dirname(fileURLToPath(import.meta.url));
const bundlePath = join(here, '..', 'dist', 'scroll-anim-fallback.umd.js');

/**
 * Evaluate the UMD bundle the way a browser `<script>` tag would, in a sandbox
 * with no module system, and return the global it attaches itself to.
 *
 * @returns {Promise<any>} The `ScrollAnimFallback` global.
 */
async function loadAsScript () {
  const code = await readFile(bundlePath, 'utf8');
  const sandbox = {};
  vm.createContext(sandbox);
  vm.runInContext(code, sandbox);
  return sandbox.ScrollAnimFallback;
}

describe('UMD bundle', () => {
  it('attaches a global when no module system is present', async () => {
    const lib = await loadAsScript();
    assert.ok(lib, 'expected a ScrollAnimFallback global');
  });

  it('exposes the public API surface', async () => {
    const lib = await loadAsScript();
    for (const name of ['init', 'destroy', 'refresh', 'observe', 'supportsNative']) {
      assert.equal(typeof lib[name], 'function', `missing ${name}`);
    }
  });

  it('re-exports the range math so it can be reused directly', async () => {
    const lib = await loadAsScript();
    // The sandbox is a separate realm, so compare by value rather than identity.
    assert.equal(
      JSON.stringify(lib.resolveNamedRange('cover', { subjectOffset: 1000, subjectSize: 200, scrollportSize: 800 })),
      JSON.stringify({ start: 200, end: 1200 })
    );
    assert.equal(lib.progressAt(700, { start: 200, end: 1200 }), 0.5);
  });

  it('reports no native support when CSS is unavailable', async () => {
    const lib = await loadAsScript();
    assert.equal(lib.supportsNative(), false);
  });

  it('refuses to initialise without a manifest', async () => {
    const lib = await loadAsScript();
    assert.throws(() => lib.init({}), /manifest/);
  });

  it('contains no leftover ES module syntax', async () => {
    const code = await readFile(bundlePath, 'utf8');
    assert.doesNotMatch(code, /^\s*(import|export)\s/m);
  });
});