That's not really true. Most libraries expose a callback mechanism, where the result of some IO is passed as a Javascript primitive to a callback function that you provide. The Dumply guys used to use an API like that.
The notion of piping the output from some I/O (say, a request to S3) into the input of some other I/O (say, a currently writing HTML response) without ever referencing it is blessed by node, which has a stream type as part of its standard library. But it's far from the most common abstraction of asynchronous work.
The notion of piping the output from some I/O (say, a request to S3) into the input of some other I/O (say, a currently writing HTML response) without ever referencing it is blessed by node, which has a stream type as part of its standard library. But it's far from the most common abstraction of asynchronous work.