JSConf JP 2025
JavaScriptにおけるasync/await呼び出しのスタックトレースの困難と実装
JSConf JP 2025
Understanding Garbage Collection in JavaScriptCore From Scratch
JavaScript relies on garbage collection (GC) to reclaim memory. In this post, we will dig into JSC’s garbage collection system. Before we start, let me briefly introduce myself. I am Haoran Xu, a PhD student at Stanford University. While I have not yet contributed a lot to JSC, I found JSC a treasure of elegant compiler designs and efficient implementations, and my research is exploring ways to tr
Optimizing JavaScript Standard Library Functions in JSC
After three years working on JavaScriptCore (JSC), I recently had the opportunity to work on optimizing one of our standard library functions for the first time. I thought it’d be interesting to share what I learned about how they work in JSC and how we make them faster. How are standard library functions implemented in JSC? The JavaScript standard library functions include all the prototype funct
2020-08-04のJS: Firefox 79、Babel 7.11.0、Speculation in JavaScriptCore
JSer.info #499 - Firefox 79がリリースされました。 Firefox 79: The safe return of shared memory, new tooling, and platform updates - Mozilla Hacks - the Web developer blog Firefox 79 for developers - Mozilla | MDN 非同期処理のスタックトレースのサポート、デバッガの改善が行われています。 target=_blankのリンクに対して暗黙的にrel=noopenerと同じ扱いをするようになりました。 また、crossOriginIsolatedが有効の場合にSharedArrayBufferが利用可能になっています。 詳しくは次の記事で解説されています。 Safely reviving shared memo
Speculation in JavaScriptCore
This post is all about speculative compilation, or just speculation for short, in the context of the JavaScriptCore virtual machine. Speculative compilation is ideal for making dynamic languages, or any language with enough dynamic features, run faster. In this post, we will look at speculation for JavaScript. Historically, this technique or closely related variants has been applied successfully t
A Tour of Inline Caching with Delete
If you search for any JavaScript performance advice, a very popular recommendation is to avoid the delete operator. Today, this seems to be good advice, but why should it be vastly more expensive to delete a property than to add it? The goal of my internship at Apple this winter was to improve the performance of the delete operator in JavaScriptCore. This has given me the opportunity to learn abou
A New Bytecode Format for JavaScriptCore
In revision r237547 we introduced a new bytecode format for JavaScriptCore (JSC). The goals of the new format were to improve memory usage and allow the bytecode to be cached on disk, while the previous format was optimized for interpreter throughput at the cost of memory usage. In this post, we will start with a quick overview of JSC’s bytecode, key aspects of the old bytecode format and the opti
Micro-benchmarking is Hard (Inside Frontend 2, 2018 Feb)
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Concurrent JavaScript: It can work!
With the recent addition of SharedArrayBuffer, concurrency is finding its way into the JavaScript language. This addition allows JavaScript programs to perform concurrent access to SharedArrayBuffer objects. WebKit supports SharedArrayBuffer and it has full optimization support in our compiler pipeline. Unfortunately, JavaScript does not allow any objects other than SharedArrayBuffer to be shared.
WebKit/PerformanceTests/ARES-6/Air at main · WebKit/WebKit
Air.js is an ES6 benchmark. It tries to faithfully use new features like arrow functions, classes, for-of, and Map/Set, among others. Air.js doesn't avoid any features out of fear that they might be slow, in the hope that we might learn how to make those features fast by looking at how Air.js and other benchmarks use them. This documents the motivation, design, and license of Air.js. To run Air.js
ES6 Feature Complete
As of r202125, JavaScriptCore supports all of the new features in the ECMAScript 6 (ES6) language specification. All of the new ES6 features are available in the latest WebKit Nightly and Safari Technology Preview. While we have an implementation of modules, no web-facing API has been finalized yet. ES6 adds a huge number of great features to the JavaScript language and all the JavaScriptCore cont
Introducing the B3 JIT Compiler
As of r195562, WebKit’s FTL JIT (Faster Than Light Just In Time compiler) now uses a new backend on OS X. The Bare Bones Backend, or B3 for short, replaces LLVM as the low-level optimizer in the FTL JIT. While LLVM is an excellent optimizer, it isn’t specifically designed for the optimization challenges of dynamic languages like JavaScript. We felt that we could get a bigger speed-up if we combine
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https://tlog.quasinomial.net/blog/dive-into-jsc/
GitHub - microsoft/playwright: Playwright is a framework for Web Testing and Automation. It allows testing Chromium, Firefox and WebKit with a single API.
182233 – [JSC] Implement trimStart and trimEnd
180190 – [DFG][FTL] operationHasIndexedProperty does not consider negative int32_t
GitHub - mbbill/JSC.js: JavaScriptCore on WebAssembly
Assembly Intermediate Representation
Towards PhantomJS 2.5 · Issue #14458 · ariya/phantomjs
BareBonesBackend – WebKit