happy-dom 20.11.2: Initialize Happy DOM with options and populate markup via document.write or window.DOMParser rather than passing HTML strings to new Window or invoking standalone DOMParser

# happy-dom Window Instantiation and HTML Parsing

## Prior Search Results

A search for known solutions for `happy-dom` returned three unrelated samples:
- `sha256:e949d296b4b86f64c795f4aaf4915e41f0e6d78206d3732bfffc80877456b1a3` (Vitest 4 test environment globals and docblock precedence)
- `sha256:ffbf1189d6c67b17effd53b4f30bb520e3a01b2c792450fda6198ef4c832f34e` (React 19 server metadata hoisting)
- `sha256:82cb4df6ef197197d50a5f2da59ac8c68181ad3387e06b4a023e6aaac0ed58a9` (yaml v2 boolean parsing)

None covered DOM instantiation or HTML parsing entrypoint traps in `happy-dom`.

## Failure Modes

Passing an HTML markup string to `new Window(html)` fails silently with an empty `document.body.innerHTML` and `null` element queries, while calling `parseFromString()` on a standalone `new DOMParser()` fails loudly with `TypeError: Cannot read properties of undefined (reading 'HTMLDocument')`.

{"case":{"believed":"Passing an HTML string to new Window(html) initializes the document markup, or instantiating new DOMParser() parses HTML strings into a DOM tree.","caseId":"case:sha256:a236542ae77b522b60ed6a2472615aaa2ef3c997c99af200491e2d392bcd8aeb","contract":["new Window(html) ignores string arguments because the constructor expects an options object, leaving document.body.innerHTML empty and getElementById returning null.","new DOMParser() imported standalone from happy-dom throws TypeError on parseFromString due to missing Window context binding.","window.document.write(html) on an existing Window instance parses the HTML string into the active document.","new window.DOMParser() bound to a Window instance successfully parses HTML into a new HTMLDocument."],"goal":"Initialize Happy DOM with options and populate markup via document.write or window.DOMParser rather than passing HTML strings to new Window or invoking standalone DOMParser","kind":"HOW","packages":["pkg:npm/happy-dom@20.11.2"],"schemaVersion":1,"symbols":["Window","DOMParser"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","ecosystem":"npm","executionContext":"node","language":"node","os":"linux","packageManager":"npm","runtime":"node","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/happy-dom@20.11.2"],"schemaVersion":1,"symbols":["Window","DOMParser"],"verifierAdapter":"node-typescript@1"}

{
  "name": "npm-happy-dom-api",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "npm-happy-dom-api",
      "version": "1.0.0",
      "license": "ISC",
      "dependencies": {
        "happy-dom": "^20.11.2"
      }
    },
    "node_modules/@types/node": {
      "version": "26.2.0",
      "resolved": "https://registry.npmjs.org/@types/node/-/node-26.2.0.tgz",
      "integrity": "sha512-5IviulTZeRNp2vAJ514cc/HUlY5nZ9fCbq9DMyC52BrhFZACo3nI0R7qBxhQmo/d27NFe96ur/b7Wwxklda+kg==",
      "license": "MIT",
      "dependencies": {
        "undici-types": "~8.3.0"
      }
    },
    "node_modules/@types/whatwg-mimetype": {
      "version": "3.0.2",
      "resolved": "https://registry.npmjs.org/@types/whatwg-mimetype/-/whatwg-mimetype-3.0.2.tgz",
      "integrity": "sha512-c2AKvDT8ToxLIOUlN51gTiHXflsfIFisS4pO7pDPoKouJCESkhZnEy623gwP9laCy5lnLDAw1vAzu2vM2YLOrA==",
      "license": "MIT"
    },
    "node_modules/@types/ws": {
      "version": "8.18.1",
      "resolved": "https://registry.npmjs.org/@types/ws/-/ws-8.18.1.tgz",
      "integrity": "sha512-ThVF6DCVhA8kUGy+aazFQ4kXQ7E1Ty7A3ypFOe0IcJV8O/M511G99AW24irKrW56Wt44yG9+ij8FaqoBGkuBXg==",
      "license": "MIT",
      "dependencies": {
        "@types/node": "*"
      }
    },
    "node_modules/buffer-image-size": {
      "version": "0.6.4",
      "resolved": "https://registry.npmjs.org/buffer-image-size/-/buffer-image-size-0.6.4.tgz",
      "integrity": "sha512-nEh+kZOPY1w+gcCMobZ6ETUp9WfibndnosbpwB1iJk/8Gt5ZF2bhS6+B6bPYz424KtwsR6Rflc3tCz1/ghX2dQ==",
      "license": "MIT",
      "dependencies": {
        "@types/node": "*"
      },
      "engines": {
        "node": ">=4.0"
      }
    },
    "node_modules/entities": {
      "version": "7.0.1",
      "resolved": "https://registry.npmjs.org/entities/-/entities-7.0.1.tgz",
      "integrity": "sha512-TWrgLOFUQTH994YUyl1yT4uyavY5nNB5muff+RtWaqNVCAK408b5ZnnbNAUEWLTCpum9w6arT70i1XdQ4UeOPA==",
      "license": "BSD-2-Clause",
      "engines": {
        "node": ">=0.12"
      },
      "funding": {
        "url": "https://github.com/fb55/entities?sponsor=1"
      }
    },
    "node_modules/happy-dom": {
      "version": "20.11.2",
      "resolved": "https://registry.npmjs.org/happy-dom/-/happy-dom-20.11.2.tgz",
      "integrity": "sha512-7MB+bJLkxu3SowAfBJbjW+c55kNz5tkR45gu2qzrxznezhLeN5YIlJbwUgSzlGc+qWoZ8Ykg71H5ezz69xixrw==",
      "license": "MIT",
      "dependencies": {
        "@types/node": ">=20.0.0",
        "@types/whatwg-mimetype": "^3.0.2",
        "@types/ws": "^8.18.1",
        "buffer-image-size": "^0.6.4",
        "entities": "^7.0.1",
        "whatwg-mimetype": "^3.0.0",
        "ws": "^8.21.0"
      },
      "engines": {
        "node": ">=20.0.0"
      }
    },
    "node_modules/undici-types": {
      "version": "8.3.0",
      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-8.3.0.tgz",
      "integrity": "sha512-j375ScV60dom+YkPFIfTLcOiPxkN/buHz5GobjLhixFuANaNs3C9l4GmrWqejgXWJ7BbJcFYpTEUkS1Ge8bpZQ==",
      "license": "MIT"
    },
    "node_modules/whatwg-mimetype": {
      "version": "3.0.0",
      "resolved": "https://registry.npmjs.org/whatwg-mimetype/-/whatwg-mimetype-3.0.0.tgz",
      "integrity": "sha512-nt+N2dzIutVRxARx1nghPKGv1xHikU7HKdfafKkLNLindmPU/ch3U31NOCGGA/dmPcmb1VlofO0vnKAcsm0o/Q==",
      "license": "MIT",
      "engines": {
        "node": ">=12"
      }
    },
    "node_modules/ws": {
      "version": "8.21.3",
      "resolved": "https://registry.npmjs.org/ws/-/ws-8.21.3.tgz",
      "integrity": "sha512-201TZ/kPWxoPr/OKWjquZR1SWKXcvxdH+e1xrx89b3YbmzLMFCLfnaG1HFIgWzJOEWZ7MvpK++odZufgYR50Rw==",
      "license": "MIT",
      "engines": {
        "node": ">=10.0.0"
      },
      "peerDependencies": {
        "bufferutil": "^4.0.1",
        "utf-8-validate": ">=5.0.2"
      },
      "peerDependenciesMeta": {
        "bufferutil": {
          "optional": true
        },
        "utf-8-validate": {
          "optional": true
        }
      }
    }
  }
}

{
  "name": "npm-happy-dom-api",
  "version": "1.0.0",
  "type": "module",
  "dependencies": {
    "happy-dom": "20.11.2"
  }
}

import { Window, DOMParser } from 'happy-dom';
import assert from 'node:assert/strict';

// Trap 1: Callers passing an HTML string to new Window(html) expecting the document to be populated.
// Window constructor only takes an options object ({ url, width, height, console, settings });
// string arguments are ignored and the document body remains empty.
const html = '<div id="app"><span>Hello World</span></div>';
const windowInstance = new Window(html);

assert.strictEqual(
  windowInstance.document.body.innerHTML,
  '',
  'new Window(html) does not populate document body because string argument is ignored as options'
);
assert.strictEqual(
  windowInstance.document.getElementById('app'),
  null,
  'getElementById returns null when HTML was passed as a string to new Window'
);

// Trap 2: Callers importing DOMParser from top-level package and instantiating standalone.
// DOMParser requires an internal Window binding; standalone instances lack this[PropertySymbol.window]
// and throw a TypeError when accessing undefined.HTMLDocument.
const standaloneParser = new DOMParser();
assert.throws(
  () => standaloneParser.parseFromString(html, 'text/html'),
  {
    name: 'TypeError',
    message: "Cannot read properties of undefined (reading 'HTMLDocument')"
  },
  'new DOMParser() standalone throws TypeError when parsing without a bound Window context'
);

// Correct approach 1: Populate an existing Window using document.write(html)
const populatedWindow = new Window();
populatedWindow.document.write(html);

assert.strictEqual(
  populatedWindow.document.body.innerHTML,
  html,
  'window.document.write parses and populates HTML into the document body'
);
assert.strictEqual(
  populatedWindow.document.getElementById('app')?.textContent,
  'Hello World',
  'Elements are accessible in DOM tree after document.write'
);

// Correct approach 2: Use DOMParser instantiated from an active Window instance
const boundParser = new populatedWindow.DOMParser();
const parsedDocument = boundParser.parseFromString(html, 'text/html');

assert.strictEqual(
  parsedDocument.body.innerHTML,
  html,
  'new window.DOMParser() successfully parses HTML string into a separate HTMLDocument'
);
assert.strictEqual(
  parsedDocument.getElementById('app')?.textContent,
  'Hello World',
  'Elements are queryable from DOMParser-created document'
);