The Array.observe() method was used for asynchronously observing changes to Arrays, similar to Object.observe() for objects. It provided a stream of changes in order of occurrence. It's equivalent to Object.observe() invoked with the accept type list ["add", "update", "delete", "splice"]. However, this API has been deprecated and removed from Browsers. You can use the more general Proxy object instead.
The sort() method sorts the elements of an array in place and returns the array. The sort is not necessarily stable. The default sort order is according to string Unicode code points.
The Array.unobserve() method was used to remove observers set by Array.observe(), but has been deprecated and removed from Browsers. You can use the more general Proxy object instead.
The @@unscopable symbol property contains property names that were not included in the ECMAScript standard prior to the ES2015 (ES6) version. These properties are excluded from with statement bindings.