singleordefault.md

Rx.Observable.prototype.singleOrDefault(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.

Arguments

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.

Returns

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

Example

/* Without a predicate but default value */
var source = Rx.Observable.empty()
    .singleOrDefault(null, 42);

var subscription = source.subscribe(
    function (x) {
        console.log('Next: ' + x);
    },
    function (err) {
        console.log('Error: ' + err);
    },
    function () {
        console.log('Completed');
    });

// => Next: 42
// => Completed

/* With a predicate */
var source = Rx.Observable.range(0, 10)
    .singleOrDefault(function (x, idx, obs) { return x ===  1; }, 0);

var subscription = source.subscribe(
    function (x) {
        console.log('Next: ' + x);
    },
    function (err) {
        console.log('Error: ' + err);
    },
    function () {
        console.log('Completed');
    });

// => Next: 1
// => Completed

Location

File:

• /src/core/linq/observable/singleordefault.js

Dist:

• rx.all.js
• rx.all.compat.js
• rx.aggregates.js

Prerequisites:

• rx.lite.js | rx.compat.js | rx.lite.js | rx.lite.compat.js

NPM Packages:

• rx

NuGet Packages:

• RxJS-All
• RxJS-Aggregates

Unit Tests:

• /tests/observable/singleordefault.js