DOM parity

Chrome is the oracle. 234 features — interfaces, members and behaviours — are put to all four runtimes, and 121 behaviour cases run the same code in each.

Runtime	Agrees with Chrome
esdev	217 / 234	93%
jsdom	184 / 234	79%
happy-dom	185 / 234	79%

By area

Area	Features	esdev	jsdom	happy-dom
tree	55	55	49	44
traversal	14	13	13	11
selectors	14	14	14	13
cascade	26	23	12	17
window	36	29	24	26
events	26	24	22	25
components	32	32	20	20
parsing	13	9	12	11
forms	18	18	18	18

Behaviour cases

119 of 121 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
list-interfaces-iterate-as-web-idl-declares	tree	yes	no	no
details-dialog-and-popover-toggle-alike	events	yes	no	no
a-removed-subtree-stays-observed-until-delivery	events	yes	no	no
an-observer-that-throws-is-reported-and-the-rest-still-run	events	yes	yes	yes
a-click-runs-activation-behaviour-however-it-is-dispatched	events	yes	no	no
keyboard-and-mouse-events-carry-their-modifiers	events	yes	yes	no
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
an-equal-specificity-tie-goes-to-the-later-sheet	cascade	yes	no	no
floats-positioned-boxes-and-flex-items-are-blockified	cascade	yes	no	no
inner-text-is-the-rendered-text	cascade	yes	no	no
media-lists-and-grouping-rules-are-their-interfaces	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
html-names-are-case-insensitive	tree	yes	yes	yes
bare-constructors-and-fragment-lookups	tree	yes	no	yes
a-radio-group-is-exclusive-on-the-checked-setter	forms	yes	yes	yes
escapes-in-an-identifier	selectors	yes	yes	no
an-unknown-property-is-not-a-declaration	cascade	yes	no	no
a-node-iterator-walks-and-steps-back	traversal	yes	yes	no
a-secondary-document-is-a-whole-document	tree	yes	yes	no
reaction-order-on-creation-and-connection	components	yes	yes	yes
an-existing-element-upgrades-when-it-is-defined	components	yes	yes	no
parsed-children-upgrade-in-tree-order	components	yes	yes	yes
the-registry-answers-about-a-definition	components	yes	yes	no
an-element-can-be-upgraded-on-demand	components	yes	yes	no
constants-node-values-and-odd-nodes-serialize	tree	yes	no	no
every-way-an-attribute-changes-is-one-change	tree	yes	no	no
form-and-select-collections-are-their-interfaces	tree	yes	yes	no
character-data-is-edited-in-place	tree	yes	no	no
a-range-edits-text-through-character-data	tree	yes	yes	no
slots-assign-and-flatten	components	yes	yes	no
flattening-recurses-through-a-slotted-slot	components	yes	yes	no
a-slot-reports-a-change	components	yes	yes	yes
internals-reflect-aria-and-form-state	components	yes	no	no
a-clonable-shadow-root-is-cloned	components	yes	no	yes
shadow-styles-reach-the-host-and-the-slotted	components	yes	no	no
a-constructor-is-refused-when-it-misbehaves	components	yes	yes	no
an-element-moved-between-documents-is-adopted	components	yes	yes	no
attributes-report-their-namespace-and-old-value	components	yes	yes	no
a-shadow-host-refuses-a-second-root-and-the-wrong-element	components	yes	yes	no
focus-inside-a-root-is-reported-from-both-sides	components	yes	yes	yes
an-event-is-retargeted-and-a-closed-root-hides-its-path	components	yes	yes	no
aria-reflects-through-attributes-and-internals	components	yes	yes	no
a-slot-change-follows-the-slot-attribute	components	yes	yes	yes
a-template-holds-a-component-and-clones-it	components	yes	no	no
adoption-and-a-shadow-sweep-report-once	components	yes	yes	no
a-closed-root-serializes-when-it-is-asked-for	components	yes	no	no
a-reset-clears-a-custom-elements-value	components	yes	no	no
a-disabled-attribute-and-a-throwing-constructor	components	yes	no	no
moveBefore-keeps-state-and-connection	tree	yes	no	no
a-document-is-parsed-from-markup	parsing	yes	no	no
a-dialog-opens-closes-and-returns	components	yes	no	no
a-popover-toggles-and-reports-its-state	components	yes	no	no
a-command-button-acts-on-the-element-it-names	components	yes	no	no
an-attribute-name-is-lowercased-for-html-only	tree	yes	yes	yes
a-document-has-no-text-content	tree	yes	yes	no
internal-work-does-not-read-the-attributes-accessor	tree	yes	yes	yes
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
cancel-bubble-is-the-stop-propagation-flag	events	yes	yes	no
nodes-stringify-as-their-interface	tree	yes	no	no
svg-elements-get-their-own-interface	parsing	yes	no	yes
a-customized-built-in-upgrades-its-built-in	components	yes	no	no
custom-properties-substitute-into-computed-values	cascade	yes	no	no
a-value-a-property-cannot-take-is-dropped	cascade	yes	no	no
shorthands-expand-into-longhands	cascade	yes	no	no
named-access-on-the-window	tree	yes	yes	no
an-inline-declaration-holds-its-longhands	cascade	yes	no	no
a-controls-value-is-filtered-not-rewritten	forms	yes	no	no
interface-members-can-be-redefined	tree	yes	yes	yes
an-attribute-handler-is-compiled-and-a-throw-is-reported	events	yes	no	no
a-colour-resolves-when-it-is-computed	cascade	yes	no	no
a-value-is-checked-against-the-property	cascade	yes	no	no
colour-functions-are-canonical	cascade	yes	no	no
lengths-are-absolute-when-they-can-be	cascade	yes	no	no
the-layered-shorthands-expand-too	cascade	yes	no	no
a-computed-shorthand-comes-from-its-longhands	cascade	yes	no	no
a-declaration-block-holds-longhands	cascade	yes	no	no
every-html-name-has-its-interface	tree	yes	yes	yes
a-template-content-lives-in-its-own-document	tree	yes	yes	no

Closer to Chrome than an emulator

64 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
innerText	yes	no	yes
document.hasFocus()	yes	no	yes
implementation.createDocument	`svg/http://www.w3.org/2000/svg`	`svg/http://www.w3.org/2000/svg`	`html/http://www.w3.org/1999/xhtml`
unknown property is undefined	`undefined/false/false`	`undefined/false/undefined`	`undefined/false/true`
keyword initial values	`none,1,visible,0px,auto`	`,,,,`	`,,,,`
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
createEvent by interface name	`Event/InvalidStateError/probe-created/true`	`Event/InvalidStateError/probe-created/true`	`Event/dispatched/probe-created/true`
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
one constructor, one name	`NotSupportedError`	`NotSupportedError`	`DOMException`
node.assignedSlot	yes	yes	no
attachShadow refuses a non-host	`NotSupportedError`	`NotSupportedError`	`attached`
:host and ::slotted	`rgb(9, 9, 9)/italic`	`rgb(0, 0, 0)/`	`rgb(9, 9, 9)/normal`
ARIA reflects	`button/Save/null`	`button/Save/null`	`button/null/undefined`
formDisabledCallback	`true`	`none`	`none`
a clonable root is cloned	`<i>x</i>`	`no root`	`<i>x</i>`
template content is inert	no	`throws:TypeError`	no
document.textContent	`null/HTML`	`null/HTML`	`/HTML`
Element.moveBefore	`1/0/kept`	`missing`	`missing`
Document.parseHTMLUnsafe	`<i>in</i>`	`missing`	`missing`
dialog.show and close	`true/false/ok`	`missing`	`true/false/ok`
popover methods	`auto/true/false`	`missing`	`missing`
CommandEvent	`show-popover/true`	`missing`	`missing`
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)`	`throws:TypeError`	`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
resolved font size	`32px`	`2em`	`16px`
structuredClone	yes	no	no
fetch	yes	no	yes
WebSocket	yes	yes	no
Worker	yes	no	no
URL.createObjectURL	yes	no	yes
alert	yes	yes	no
MathMLElement	yes	no	no
SVGGeometryElement	yes	no	yes
showPopover	yes	no	no
dialog.showModal	yes	no	yes

Differences from Chrome

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

Legacy or superseded by a modern API that is implemented.

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

Refused by name: the modern interface name is accepted, and the HTML4 alias is answered with the constructor to use instead.

Feature	Chrome	esdev
createEvent refuses the HTML4 aliases	`created`	`NotSupportedError`

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

Feature	Chrome	esdev
getBoundingClientRect measures	`measured`	`zero`
offsetWidth measures	`measured`	`zero`

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

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

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
XMLHttpRequest	yes	no
Image	yes	no
canvas.getContext	`context`	`missing`
iframe.contentWindow	`window`	`null`