if.md

This is RxJS v 4. Find the latest version here

Rx.Observable.if(condition, thenSource, [elseSource])

Rx.Observable.ifThen(condition, thenSource, [elseSource]) DEPRECATED

Ⓢ

Determines whether an observable collection contains values. There is an alias for this method called ifThen for browsers <IE9

Arguments

1. condition (Function): The condition which determines if the thenSource or elseSource will be run.
2. thenSource (Observable): thenSource The observable sequence that will be run if the condition function returns true.
3. [elseSource] (Observable|Scheduler): The observable sequence that will be run if the condition function returns false. If this is not provided, it defaults to Rx.Observabe.Empty with the specified scheduler.

Returns

(Observable): The generated sequence.

Example

// This uses and only then source
var shouldRun = true;

var source = Rx.Observable.if(
    function () { return shouldRun; },
    Rx.Observable.return(42)
);

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

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

// The next example uses an elseSource
var shouldRun = false;

var source = Rx.Observable.if(
    function () { return shouldRun; },
    Rx.Observable.return(42),
    Rx.Observable.return(56)
);

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

// => Next: 56
// => Completed

Location

File:

• /src/core/linq/observable/if.js

Dist:

• rx.all.js
• rx.experimental.js

Prerequisites:

• If using rx.experimental.js - rx.js | rx.compat.js | rx.lite.js | rx.lite.compat.js

NPM Packages:

• rx

NuGet Packages:

• RxJS-Experimental

Unit Tests:

• /tests/observable/if.js