Rx.Observable.prototype.first([predicate], [thisArg], [defaultValue])
, Rx.Observable.prototype.first([settings])
Returns the first element of an observable sequence that satisfies the condition in the predicate, or a default value if no such element exists. If no default value is given, then onError
will be called.
参数
Rx.Observable.prototype.first([predicate], [thisArg], [defaultValue])
[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 asthis
when executing the predicate.[defaultValue]
(Any
): Default value if no such element exists.
Rx.Observable.prototype.first([settings])
[settings]
(Object
): An object with the following fields[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 asthis
when executing the predicate.[defaultValue]
(Any
): Default value if no such element exists.
返回值
(Observable
): An observable sequence that contains elements from the input sequence that satisfy the condition.
例
No Match
Without a predicate
With a predicate
/* With a default value */
var source = Rx.Observable.range(0, 10)
.first({
predicate: function (x, idx, obs) { return x > 10; },
defaultValue: 42
});
var subscription = source.subscribe(
function (x) {
console.log('Next: %s', x);
},
function (err) {
console.log('Error: %s', err);
},
function () {
console.log('Completed');
});
// => Next: 42
// => Completed