el.style (CSSStyleDeclaration) and el.dataset (DOMStringMap) were plain
Proxies with only get/set traps, so `'color' in el.style`, `Object.keys
(el.style)`, `'foo' in el.dataset`, and `Object.keys(el.dataset)` all
failed, and Object.keys(el.style) leaked the internal `_props` (issue
#356). cssText also serialized camelCase names without a trailing
semicolon.
Add has / ownKeys / getOwnPropertyDescriptor traps to both proxies so the
`in` operator and enumeration behave like real CSSOM. CSSStyleDeclaration
now stores properties by their dashed name (matching the spec), so
el.style.fontSize and getPropertyValue('font-size') stay in sync, and
cssText serializes dashed names with a trailing semicolon. A known CSS
property list backs `in`/enumeration so feature detection ('object-fit'
in el.style) works for unset properties.
Closes#356.
SGavrl
ad7a7a93d1