What are streams?

Learn the stream concept and its types.

What are streams?

A stream is a data structure that processes data piece by piece. Instead of loading all data into memory at once, it flows in small slices called chunks. This saves memory with large files or continuous data.

In Node.js streams come from the stream module. For example Readable.from(["a", "b"]) creates a readable stream from an array. Streams appear in http requests, fs file reading and process.stdout. Streaming data is the standard way to process large data from disk or network piece by piece.

Stream types

Node.js has four core stream types. Readable flows in the reading direction (source → program). Writable flows in the writing direction (program → target). Duplex both reads and writes (two-way). Transform reads, transforms the data and writes.

All are imported from the stream module: const { Readable, Writable, Transform } = require("stream");. Readable.from(array) is the simplest way to create a readable stream; it turns an array into a list of chunks. We will examine each type in the following lessons.

Exercise Create a Readable

Import Readable from the stream module. Create a readable stream named stream with Readable.from(["data"]). Print "Stream ready" with console.log.

Show example solution

const { Readable } = require("stream");
const stream = Readable.from(["data"]);
console.log("Stream ready");

Test yourself

What is the main benefit of using streams?
```
Readable.from([...])
```
- Makes the code shorter
- Catches errors automatically
- Processes large data chunk by chunk and saves memory
- Carries only numbers, not text
Show answer

Processes large data chunk by chunk and saves memory — Streams process data in chunks to save memory.

Complete the module name

const { Readable } = require("____");

Show answer

const { Readable } = require("stream");

Match each type to its direction

Readable

Reads from a source
Writable

Writes to a target
Transform

Transforms then writes
Duplex

Flows both ways

Next lesson: Readable stream

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