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`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

condition (Function): The condition which determines if the thenSource or elseSource will be run.
thenSource (Observable): thenSource The observable sequence that will be run if the condition function returns true.
[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