Rx.Observable.prototype.firstOrDefault(predicate, [defaultValue], [thisArg])

Returns the first element of an observable sequence that satisfies the condition in the predicate, or a default value if no such element exists.

参数

1. predicate (Function): A predicate function to evaluate for elements in the source sequence. The callback is called with the following information:
   1. the value of the element
   2. the index of the element
   3. the Observable object being subscribed
2. [defaultValue] (Any): The default value if no such element exists. If not specified, defaults to null.
3. [thisArg] (Any): Object to use as this when executing the predicate.

返回值

(Observable): An observable sequence that contains elements from the input sequence that satisfy the condition.

例

Without a predicate but default value

With a predicate