@tiptap/extension-underline 3.11.0: extend

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify @tiptap/extension-underline.extend in pkg:npm/%40tiptap/extension-underline@3.11.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40tiptap/extension-underline@3.11.0
Demonstrate these symbols/APIs:
  - @tiptap/extension-underline.extend

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

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import { Underline } from '@tiptap/extension-underline';

/**
 * Creates an extended Underline mark extension with custom options and rendering.
 *
 * @param {object} [config={}] - Extension override configuration.
 * @returns {object} Extended mark extension.
 */
export function createExtendedUnderline(config = {}) {
  return Underline.extend({
    name: config.name || 'customUnderline',
    addOptions() {
      return {
        ...this.parent?.(),
        style: 'solid',
        color: 'currentColor',
        ...(config.options || {})
      };
    },
    renderHTML({ HTMLAttributes }) {
      if (config.renderHTML) {
        return config.renderHTML({ HTMLAttributes });
      }
      return [
        'u',
        {
          class: 'custom-underline',
          ...HTMLAttributes
        },
        0
      ];
    }
  });
}

export { Underline };
export default Underline;

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{
  "name": "sample-tiptap-extension-underline-extend",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "license": "MIT-0",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "@tiptap/extension-underline": "3.11.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify @tiptap/extension-underline.extend in pkg:npm/%40tiptap/extension-underline@3.11.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40tiptap/extension-underline@3.11.0"
  ],
  "symbols": [
    "@tiptap/extension-underline.extend"
  ]
}

import assert from 'node:assert/strict';
import { Underline } from '@tiptap/extension-underline';
import { createExtendedUnderline } from '../index.mjs';

// 1. Underline exports extend function on the mark extension object
assert.equal(typeof Underline, 'object', 'Underline must be an object');
assert.equal(typeof Underline.extend, 'function', 'Underline.extend must be a function');
assert.equal(Underline.name, 'underline', 'Underline default name is underline');
assert.equal(Underline.type, 'mark', 'Underline type is mark');

// 2. Underline.extend() creates a new mark extension with overridden name
const NamedUnderline = Underline.extend({
  name: 'highlightedUnderline'
});
assert.equal(typeof NamedUnderline, 'object');
assert.equal(NamedUnderline.name, 'highlightedUnderline');
assert.equal(NamedUnderline.type, 'mark');
assert.notEqual(NamedUnderline, Underline, 'Extended extension must be a distinct instance');

// 3. Underline.extend() extends options via addOptions while preserving parent default options
const CustomOptionsUnderline = Underline.extend({
  name: 'customOptionsUnderline',
  addOptions() {
    return {
      ...this.parent?.(),
      color: 'blue',
      thickness: '2px'
    };
  }
});
assert.deepEqual(
  CustomOptionsUnderline.options,
  {
    HTMLAttributes: {},
    color: 'blue',
    thickness: '2px'
  },
  'Options must include parent options and newly added options'
);

const helperExt = createExtendedUnderline({
  name: 'helperUnderline',
  options: { color: 'green' }
});
assert.equal(helperExt.name, 'helperUnderline');
assert.deepEqual(
  helperExt.options,
  {
    HTMLAttributes: {},
    style: 'solid',
    color: 'green'
  }
);

// 4. Underline.extend() allows overriding renderHTML to customize rendered output
const CustomRenderUnderline = Underline.extend({
  name: 'customRenderUnderline',
  renderHTML({ HTMLAttributes }) {
    return ['span', { class: 'custom-underline-span', ...HTMLAttributes }, 0];
  }
});
const rendered = CustomRenderUnderline.config.renderHTML.call(
  { options: CustomRenderUnderline.options },
  { HTMLAttributes: { id: 'u-custom' } }
);
assert.deepEqual(
  rendered,
  ['span', { class: 'custom-underline-span', id: 'u-custom' }, 0],
  'renderHTML must return custom tag and attributes'
);

// 5. Underline.extend() supports chained extension creating further specialized extensions
const BaseExtended = Underline.extend({
  name: 'baseUnderline',
  addOptions() {
    return {
      ...this.parent?.(),
      level: 1
    };
  }
});
const ChainedExtended = BaseExtended.extend({
  name: 'chainedUnderline',
  addOptions() {
    return {
      ...this.parent?.(),
      level: 2,
      active: true
    };
  }
});
assert.equal(ChainedExtended.name, 'chainedUnderline');
assert.deepEqual(
  ChainedExtended.options,
  {
    HTMLAttributes: {},
    level: 2,
    active: true
  },
  'Chained extended extension must inherit and override options'
);

// 6. An extended Underline extension can be configured with configure() to override options
const configured = ChainedExtended.configure({
  level: 3,
  HTMLAttributes: { 'data-level': '3' }
});
assert.equal(configured.name, 'chainedUnderline');
assert.deepEqual(
  configured.options,
  {
    HTMLAttributes: { 'data-level': '3' },
    level: 3,
    active: true
  },
  'Configured extended extension must reflect overridden options'
);

console.log('All @tiptap/extension-underline.extend contract tests passed successfully.');