DOM parity

Chrome is the oracle. 192 features — interfaces, members and behaviours — are put to all four runtimes, and 46 behaviour cases run the same code in each.

Runtime	Agrees with Chrome
esdev	168 / 192	88%
jsdom	155 / 192	81%
happy-dom	158 / 192	82%

By area

Area	Features	esdev	jsdom	happy-dom
tree	44	43	40	36
traversal	13	11	12	10
cascade	24	20	12	17
events	24	23	20	24
components	17	17	12	13
parsing	12	8	12	11
selectors	13	13	13	12
forms	14	14	14	14
window	31	19	20	21

Behaviour cases

44 of 46 cases match Chrome exactly, and 2 is a documented limit.

Case	Area	esdev	jsdom	happy-dom
append-and-replace-children	tree	yes	yes	yes
fragment-contents-move-on-append	tree	yes	yes	yes
deep-clone-is-independent	tree	yes	yes	yes
collections-stay-live	tree	yes	yes	yes
capturing-and-bubbling-order	events	yes	yes	yes
cancelled-event-returns-false	events	yes	yes	yes
inline-handlers-run-for-modern-events	events	yes	yes	yes
once-listener-runs-once	events	yes	yes	yes
stopped-propagation-does-not-reach-parent	events	yes	yes	yes
fragment-serializes-text-and-attributes	parsing	yes	yes	yes
raw-text-is-not-parsed-as-elements	parsing	yes	yes	yes
svg-attributes-and-self-closing-children	parsing	yes	yes	no
namespace-attribute-access-and-replacement	tree	yes	yes	yes
dataset-reflects-data-attributes	tree	yes	yes	no
create-element-ns-preserves-identity	tree	yes	yes	yes
omitted-tags-html-allows-are-filled-in	parsing	yes	yes	no
table-collections-follow-the-section-order	tree	yes	yes	no
fragment-structure-follows-its-context-element	parsing	yes	yes	yes
malformed-markup-is-a-strict-esdev-limit	parsing	no	yes	yes
compound-and-attribute-selector	selectors	yes	yes	yes
logical-selector-list	selectors	yes	yes	yes
structural-selector	selectors	yes	yes	yes
invalid-selector-throws-syntax-error	selectors	yes	yes	no
nth-child-counts-only-the-of-list	selectors	yes	no	yes
defined-pseudo-class-follows-the-definition	components	yes	yes	no
adjacent-insertion-lands-at-four-positions	tree	yes	yes	yes
declarative-shadow-root-attaches-only-through-set-html-unsafe	components	yes	no	no
form-associated-custom-element-joins-its-form	components	yes	no	no
custom-state-matches-the-state-pseudo-class	components	yes	no	no
origin-importance-specificity-and-order-decide-the-winner	cascade	yes	yes	yes
inheritance-and-user-agent-defaults	cascade	yes	no	no
media-and-supports-conditions-gate-their-rules	cascade	yes	no	no
constructed-sheets-apply-while-adopted	cascade	yes	no	no
a-shadow-root-is-styled-by-its-own-sheets	cascade	yes	no	no
nesting-resolves-against-its-parent-rule	cascade	yes	no	no
geometry-answers-zero-and-rendering-is-knowable	cascade	no	no	no
input-indeterminate-is-non-reflecting-state	forms	yes	yes	yes
form-owner-follows-form-attribute	forms	yes	yes	yes
form-and-submitter-settings-reflect	forms	yes	no	yes
form-data-uses-successful-controls	forms	yes	yes	yes
required-control-blocks-submit	forms	yes	yes	yes
submitter-no-validate-bypasses-constraints	forms	yes	no	yes
reset-control-restores-default-value	forms	yes	yes	yes
radio-click-is-exclusive-by-form-owner	forms	yes	yes	yes
label-click-activates-nested-checkbox	forms	yes	yes	yes
disabled-fieldset-excludes-validation-and-data	forms	yes	yes	no

Closer to Chrome than an emulator

39 features where esdev matches Chrome and jsdom or happy-dom does not.

Feature	Chrome & esdev	jsdom	happy-dom
CDATASection	yes	yes	no
DOMImplementation	yes	yes	no
DOMTokenList	yes	yes	no
DOMStringMap	yes	yes	no
CharacterData in the prototype chain	`Text < CharacterData < Node < EventTarget < Object`	`Text < CharacterData < Node < EventTarget < Object`	`Text < Text < CharacterData < Node < EventTarget < Object`
document.doctype	`html`	`html`	`none`
Element.setHTMLUnsafe	yes	no	no
Element.getHTML	yes	no	yes
Element.checkVisibility	yes	no	no
StaticRange	yes	yes	no
AbstractRange	yes	yes	no
Range.getBoundingClientRect	yes	no	yes
element scroll offsets	`0,0,false`	`40,0,true`	`40,0,false`
DragEvent	yes	no	yes
ClipboardEvent	yes	no	yes
IntersectionObserver	yes	no	yes
ResizeObserver	yes	no	yes
manual slot assignment	yes	no	yes
shadow root reports clonable and serializable	`true,false`	`,`	`true,false`
setHTMLUnsafe attaches a declarative root	`attached`	`throws:TypeError`	`throws:TypeError`
attachInternals	yes	yes	no
form-associated custom element	yes	no	`throws:TypeError`
CustomStateSet	yes	no	no
omitted paragraph end tag	`<p>one</p><p>two</p>`	`<p>one</p><p>two</p>`	`<p>one<p>two</p></p>`
invalid selector throws	`SyntaxError`	`SyntaxError`	`no throw`
adoptedStyleSheets applies	`rgb(1, 2, 3)`	`rgb(0, 0, 0)`	`rgb(1, 2, 3)`
user-agent display defaults	`block,inline`	`block,inline`	`block,`
no computed style outside the tree	yes	no	yes
@media follows the viewport	`rgb(7, 7, 7)`	`rgb(0, 0, 0)`	`rgb(7, 7, 7)`
matchMedia answers	`true,false`	`throws:TypeError`	`true,false`
CSS.supports	`true,true`	`undefined,undefined`	`true,true`
CSS nesting resolves	`rgb(2, 2, 2)`	`rgb(1, 1, 1)`	``
scrollIntoView	yes	no	yes
structuredClone	yes	no	no
fetch	yes	no	yes
WebSocket	yes	yes	no
Worker	yes	no	no
URL.createObjectURL	yes	no	yes
MathMLElement	yes	no	no

Differences from Chrome

24 features, each with its reason. There are no others.

No layout: there is no box model, so there is nothing to measure or scroll.

Feature	Chrome	esdev
innerText	yes	no
getBoundingClientRect measures	`measured`	`zero`
offsetWidth measures	`measured`	`zero`

Legacy or superseded by a modern API that is implemented.

Feature	Chrome	esdev
NodeIterator	yes	no
XPathEvaluator (document.evaluate)	yes	no
TouchEvent	yes	no
XMLSerializer	yes	no
document.write	yes	no

Deliberately strict: malformed markup is refused rather than repaired.

Feature	Chrome	esdev
malformed HTML	`<p><i>unclosed</i></p>`	`throws:SyntaxError`
misnested tags	`<b><i>x</i></b>`	`throws:SyntaxError`

No rendering: the top layer, animations and transitions have nothing to paint.

Feature	Chrome	esdev
Element.animate (WAAPI)	yes	no
showPopover	yes	no
dialog.showModal	yes	no
document.startViewTransition	yes	no

Specified values only: resolving one needs layout and a font.

Feature	Chrome	esdev
resolved font size	`32px`	`2em`

Harness artifact: Chrome ran the probe on about:blank, which is an opaque, insecure origin.

Feature	Chrome	esdev
localStorage	`throws:SecurityError`	yes
crypto.randomUUID	no	yes

No host resource: this DOM reaches no network, no file and no browsing context.

Feature	Chrome	esdev
document.cookie	yes	no
XMLHttpRequest	yes	no
File / FileReader	yes	no
alert	yes	no
Image	yes	no
canvas.getContext	`context`	`missing`
iframe.contentWindow	`window`	`null`