Streams & Buffers

Streams let Node process data piece by piece as it arrives instead of loading it all into memory at once, and Buffers are the fixed-length chunks of raw binary data that streams move around.

Learn Streams & Buffers in our free Node.js course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick reference.

Part of the free Node.js course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

By the end of this lesson you'll know what a Buffer holds and how to convert it to and from text, you'll read a large file chunk by chunk with a readable stream, and you'll copy a file efficiently by piping one stream into another — all while keeping memory use flat.

What You'll Learn in This Lesson

1️⃣ Buffers: Chunks of Raw Bytes

Before streams, you need to understand what they carry. A Buffer is Node's container for raw binary data — a fixed-length sequence of bytes. Text, images, network packets: at the lowest level they're all just bytes, and a Buffer is how Node holds them.

Read the worked example below — every line is explained — then run it. Notice that printing the Buffer directly shows its bytes as hexadecimal numbers.

2️⃣ Readable Streams: Data Piece by Piece

A readable stream hands you a file (or a network response, or any source) in small chunks instead of all at once. You open one with fs.createReadStream(path) and then listen for two key events:

Why bother? Because fs.readFile loads the entire file into memory before you see a single byte. A 2 GB log file would need 2 GB of RAM. A stream processes that same file in ~64 KB chunks, so memory use stays low and constant no matter how big the file gets.

Your turn. The program below works once you fill in the three blanks marked ___ . Follow the 👉 hints, then run it and compare with the expected output.

3️⃣ Writable Streams & .pipe()

A writable stream is the opposite of a readable one: it's a destination you push chunks into . You create one with fs.createWriteStream(path) . The magic happens when you connect a readable stream to a writable one with .pipe() :

This is how you copy a multi-gigabyte file using only a tiny, constant amount of memory — the whole copy is just source.pipe(dest) .

No blanks this time — just a brief and an outline to keep you on track. Stream a file, total up the byte length of each chunk, and print the result. Write it yourself, run it, and check your output against the example in the comments.

📋 Quick Reference — Streams & Buffers

Practice quiz

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