zlib.bytesRead to zlib.bytesWritten

Migrate deprecated zlib.bytesRead property to zlib.bytesWritten for Node.js DEP0108

This codemod replaces zlib.bytesRead with zlib.bytesWritten for consistent stream property naming to handle Node.js DEP0108.

What It Does

This codemod:

• Replaces bytesRead property with bytesWritten in all zlib transform streams
• Handles both CommonJS and ESM imports
• Works with all zlib stream types (Gzip, Deflate, Inflate, etc.)

Before/After Examples

Basic Usage with Gzip

Before:

const zlib = require("node:zlib");
const gzip = zlib.createGzip();
gzip.on("end", () => {
  console.log("Bytes processed:", gzip.bytesRead);
});

After:

const zlib = require("node:zlib");
const gzip = zlib.createGzip();
gzip.on("end", () => {
  console.log("Bytes processed:", gzip.bytesWritten);
});

Statistics Object

Before:

const zlib = require("node:zlib");
const deflate = zlib.createDeflate();
deflate.on("finish", () => {
  const stats = {
    input: deflate.bytesRead,
    output: deflate.bytesWritten
  };
});

After:

const zlib = require("node:zlib");
const deflate = zlib.createDeflate();
deflate.on("finish", () => {
  const stats = {
    input: deflate.bytesWritten,
    output: deflate.bytesWritten
  };
});

Progress Tracking

Before:

const zlib = require("node:zlib");
function trackProgress(stream) {
  setInterval(() => {
    console.log(`Progress: ${stream.bytesRead} bytes`);
  }, 1000);
}

After:

const zlib = require("node:zlib");
function trackProgress(stream) {
  setInterval(() => {
    console.log(`Progress: ${stream.bytesWritten} bytes`);
  }, 1000);
}

ESM Import

Before:

import { createGzip } from "node:zlib";
const gzip = createGzip();
const bytesProcessed = gzip.bytesRead;

After:

import { createGzip } from "node:zlib";
const gzip = createGzip();
const bytesProcessed = gzip.bytesWritten;

Destructured Require

Before:

const { createGzip } = require("node:zlib");
const gzip = createGzip();
const bytes = gzip.bytesRead;

After:

const { createGzip } = require("node:zlib");
const gzip = createGzip();
const bytes = gzip.bytesWritten;

Usage

Run this codemod on your project:

npx codemod node/userland/zlib-bytesread-to-byteswritten

The property name change from bytesRead to bytesWritten may seem counterintuitive, but it aligns with the stream’s perspective: bytes written to the compression/decompression stream.

This codemod works with all zlib compression streams including createGzip(), createGunzip(), createDeflate(), createInflate(), createDeflateRaw(), createInflateRaw(), createUnzip(), and createBrotliCompress()/createBrotliDecompress().

Related Deprecations

• DEP0108: zlib.bytesRead