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.
Arguments
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.
Returns
(Observable
): An observable sequence that contains elements from the input sequence that satisfy the condition.
Example
/* Without a predicate */
var source = Rx.Observable.range(0, 10).first();
var subscription = source.subscribe(
function (x) {
console.log('Next: %s', x);
},
function (err) {
console.log('Error: %s', err);
},
function () {
console.log('Completed');
});
// => Next: 0
// => Completed
/* With a predicate */
var source = Rx.Observable.range(0, 10)
.first(function (x, idx, obs) { return x % 2 === 1; });
var subscription = source.subscribe(
function (x) {
console.log('Next: %s', x);
},
function (err) {
console.log('Error: %s', err);
},
function () {
console.log('Completed');
});
// => Next: 1
// => Completed
/* 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
Location
File:
Dist:
Prerequisites:
NPM Packages:
NuGet Packages:
Unit Tests: