javascript - .do() or .subscribe() -

i understand best practice of using .subscribe , .do methods of observables.

for example if need job after initial data loaded server

const init$: observable<mydata> = this._dataservice.getdata();  init$   .do((initialdata: mydata) => {     this.data = initialdata; // @ step initializing view   })   .switchmap(() => loadextradata)   .subscribe((extradata) => {      dosomething(extradata, this._data); // need this._data here   });  

i can same .subscribe

const init$: observable<mydata> = this._dataservice.getdata()   .sharereplay(1);  init$   .subscribe((initialdata: mydata) => {     this.data = initialdata; // @ step initializing view   })  init$   .combinelatest(loadextradata)   .subscribe(([initialdata, extradata]) => {      dosomething(extradata, initialdata); // need this._data here   });  

which 1 better , why?

the observable chain not going until use subscribe() makes connections between operators. have use subscribe() method.

the do() operator intended make side-effects.

in experience it's not possible in subscribe() , need use do() because application logic needs make actions in specific order.

so in general i'd try avoid using do() , put of logic subscribe(). if had perform actions in different order i'd use do().