Difference between the methods .pipe() and .subscr

问题:

I recently notice that I can return a value inside .pipe() but not inside .subscribe().

What is the difference between these two methods?

For example if I have this function, let's call it 'deposit', which is supposed to return the account balance, if I do this:

deposit(account, amount){
    return this.http.get('url')
    .subscribe(res => {
        return res;
    }
}

It returns an observable and if I do this:

deposit(account, amount){
    return this.http.get('url')
    .pipe(
        map(res => {
            return res;
        });
    );
}

It returns the account balance as expected.

So why?

回答1:

The pipe method is for chaining observable operators, and the subscribe is for activating the observable and listening for emitted values.

The pipe method was added to allow webpack to drop unused operators from the final JavaScript bundle. It makes it easier to build smaller files.

For example if I have this function, let's call it 'deposit', which supposed to return the account balance, if I do this:

That isn't what it returns. It returns the Subscription object created when you called Subscribe.

it returns the account balance as expected.

That isn't what it returns. It returns an Observable which uses a map operator. The map operator in your example does nothing.