Deprecate and remove: non-allowlisted Event interfaces from document.createEvent()

at a glance

why it exists

The DOM Standard explicitly lists which event interface names document.createEvent() must accept and requires NOT_SUPPORTED_ERR for everything else. Chrome historically accepted many non-standard strings for legacy compat, silently constructing a CustomEvent. This removal closes that compat gap, matches the behavior of Firefox and Safari, and removes a footgun where code that passes wrong interface names silently "worked" in Chrome but would fail cross-browser.

Interfaces with usage above 0.01% or those deemed difficult to remove immediately remain as deprecation-only (console warning) in this cycle.

the allowlist

The DOM Standard allows these event interface strings (case-insensitive):

All other strings now throw DOMException: NOT_SUPPORTED_ERR.

migration

The modern pattern uses constructors directly and doesn't need createEvent at all:

// Old — may throw in Chrome 148+
const evt = document.createEvent("SomeInterface");
evt.initEvent("click", true, true);
el.dispatchEvent(evt);

// New — use constructors
el.dispatchEvent(new MouseEvent("click", { bubbles: true, cancelable: true }));
el.dispatchEvent(new CustomEvent("my-event", { detail: { foo: "bar" } }));
el.dispatchEvent(new KeyboardEvent("keydown", { key: "Enter", bubbles: true }));

Checking whether your code is affected

// Search your codebase for createEvent calls with non-standard strings:
// grep -r 'createEvent' src/ | grep -v -i
//   'Event\|CustomEvent\|UIEvent\|MouseEvent\|KeyboardEvent\|FocusEvent\|WheelEvent\|InputEvent\|CompositionEvent'

browser support

see also

• DOM Standard — document.createEvent()
• Chromium bug tracker: issue 41228793
• chromestatus: Deprecate and remove non-allowlisted Event interfaces