Rx.Observable.prototype.last([predicate], [thisArg])

Returns the last element of an observable sequence that satisfies the condition in the predicate if specified, else the last element.
参数
predicate(Function): A predicate function to evaluate for elements in the source sequence. The callback is called with the following information:- the value of the element
- the index of the element
- the Observable object being subscribed
[thisArg](Any): Object to use asthiswhen executing the predicate.
返回值
(Observable): Sequence containing the last element in the observable sequence that satisfies the condition in the predicate.