---
title: "Bun v1.3.13: test isolation, 8x less memory for source maps, and faster gzip"
url: https://daily.dev/posts/bun-v1-3-13-test-isolation-8x-less-memory-for-source-maps-and-faster-gzip-cn7q3pa6a
source_url: https://daily.dev/posts/bun-v1-3-13-test-isolation-8x-less-memory-for-source-maps-and-faster-gzip-cn7q3pa6a
type: collection
source: "Collections"
published: 2026-04-20T07:54:29.646Z
updated: 2026-04-20T09:11:25.881Z
tags: ["javascript", "performance", "testing", "nodejs", "bun"]
reading_time: 1
upvotes: 12
comments: 1
language: en
---

> ## Documentation Index
> Fetch the complete documentation index at: https://daily.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Bun v1.3.13: test isolation, 8x less memory for source maps, and faster gzip

**[Collections](https://daily.dev/sources/collections)** · 1 min read · 12 upvotes · 1 comments

## Summary

Bun v1.3.13 ships with notable performance gains and new test runner capabilities. Four new flags — --isolate, --parallel, --shard, and --changed — give developers finer control over test execution. Memory usage drops dramatically: bun install uses ~17x less memory by streaming tarballs to disk, and source maps consume 8x less memory. gzip compression is up to 5.5x faster via zlib-ng. New features include Range request support in Bun.serve(), SHA3 hash algorithms, and WebSocket unix socket schemes. The JavaScriptCore engine received 1,316 upstream commits, and 82 reported issues were closed including Node.js compatibility fixes and memory leak patches.

## Content

Bun v1.3.13 is out with a broad set of performance improvements, new test runner flags, and Node.js compatibility fixes.

## Test runner

Four new flags make test suites faster and more flexible:

- `--isolate` runs each test file in its own environment
- `--parallel` runs test files concurrently
- `--shard` splits tests across multiple CI jobs
- `--changed` runs only tests affected by uncommitted git changes

## Memory and performance

`bun install` now streams tarballs directly to disk instead of buffering them, cutting memory usage by roughly 17x. Source maps have been rearchitected to use 8x less memory. gzip compression is up to 5.5x faster thanks to a switch to zlib-ng.

## New features

- `Bun.serve()` now supports Range requests for file-backed responses
- SHA3 hash algorithms are available in both WebCrypto and `node:crypto`
- WebSocket clients support `ws+unix://` and `wss+unix://` schemes

## Engine and compatibility

The JavaScriptCore engine was updated with 1,316 upstream commits. The release also includes dozens of Node.js compatibility fixes, crash fixes, and memory leak patches, closing 82 reported issues.

## Similar posts on daily.dev

- [Bun v1.3.6](https://daily.dev/posts/bun-v1-3-6-wx4br4zyw) · Bun · 94 upvotes · 1 comments

---

Tags: [#javascript](https://daily.dev/tags/javascript), [#performance](https://daily.dev/tags/performance), [#testing](https://daily.dev/tags/testing), [#nodejs](https://daily.dev/tags/nodejs), [#bun](https://daily.dev/tags/bun)

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