1.Hot & Cold Observables
（1）Cold Observables：在被訂閱后開始產(chǎn)生數(shù)據(jù)笨使，即這類observables序列僅在subscribe()被調(diào)用后才會(huì)推送數(shù)據(jù)抖苦；
let obs = Rx.Observable.create(observer => observer.next(Date.now()));
obs.subscribe(v => console.log('1st subscriber:' + v)); //1st subscriber: 1465990942935
obs.subscribe(v => console.log('2st subscriber:' + v)); //2nd subscriber: 1465990942936
//兩次獲得的數(shù)據(jù)不同无蜂，即observer.next(Date.now())被調(diào)用了兩次；
（2）Hot Observables：在被訂閱之前就已經(jīng)開始生成數(shù)據(jù)；
