// emit 3, 3, 3, 9, 1, 4, 5, 8, 96, 3, 66, 3, 3, 3

const source = Rx.Observable.of(3, 3, 3, 9, 1, 4, 5, 8, 96, 3, 66, 3, 3, 3);

​

// allow values until value from source equals 3, then complete

// output: [3, 3, 3]

source

 .takeWhile(it => it === 3 )

 .subscribe(val => console.log('takeWhile', val));

​

// output: [3, 3, 3, 3, 3, 3, 3]

source

 .filter(it => it === 3)

 .subscribe(val => console.log('filter', 3));

​