defer.html

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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.bootcss.com/rxjs/5.4.0/Rx.min.js"></script>
</head>

<body>
    <script>
        //eg
        /*
            var clicksOrInterval = Rx.Observable.defer(function () {
                if (Math.random() > 0.5) {
                    return Rx.Observable.fromEvent(document, 'click');
                } else {
                    return Rx.Observable.interval(1000);
                }
            });
            clicksOrInterval.subscribe(x => console.log(x));
        */
        //f-eg
        /* Using an observable sequence */
        /* Using a promise */
        // var source = Rx.Observable.defer(() => Rx.Promise.resolve(42));

        // var subscription = source.subscribe(
        //     x => console.log(`onNext: ${x}`),
        //     e => console.log(`onError: ${e}`),
        //     () => console.log('onCompleted'));

        // => onNext: 42
        // => onCompleted

        // => onNext: 42
        // => onCompleted
    </script>
</body>

</html>