Node: Up and Running

I/O

I/O is one of the core pieces that makes Node different from other frameworks. This section explores the APIs that provide nonblocking I/O in Node.

Streams

Many components in Node provide continuous output or can process continuous input. To make these components act in a consistent way, the stream API provides an abstract interface for them. This API provides common methods and properties that are available in specific implementations of streams. Streams can be readable, writable, or both. All streams are EventEmitter instances, allowing them to emit events.

Readable streams

The readable stream API is a set of methods and events that provides access to chunks of data as they are sent by an underlying data source. Fundamentally, readable streams are about emitting data events. These events represent the stream of data as a stream of events. To make this manageable, streams have a number of features that allow you to configure how much data you get and how fast.

The basic stream in Example 4-16 simply reads data from a file in chunks. Every time a new chunk is made available, it is exposed to a callback in the variable called data. In this example, we simply log the data to the console. However, in real use cases, you might either stream the data somewhere else or spool it into bigger pieces before you work on it. In essence, the data event simply provides access to the data, and you have to figure out what to do with each chunk.

Example 4-16. Creating a readable file stream

var fs ...