Ecosystem and production
The Provenance Was Valid. The Commit Was Not.
An npm provenance attestation binds a tarball to a repository, a workflow and a commit. Reading the payload shows what it never claims.
JavaScript, TypeScript, and the runtimes underneath
What JavaScript and TypeScript actually do, one layer down
JS Ledger examines JavaScript, TypeScript, and the runtimes, frameworks, and tooling behind modern web applications.
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Language internals
Your Array Chain Called the Mapper a Million Times
Two chains return the same five numbers. One calls the mapper 1,000,000 times and allocates 13.73 MB; the other calls it 13 times and allocates nothing measurable.
Runtime and performance
Four Maps Is Polymorphic. Five Is Not.
Monomorphic, polymorphic and megamorphic are counted states with a threshold of four. Here is the transition log, the V8 line that decides it, and the cost.
Ecosystem and production
require(esm) Killed the Second Build, Not the Second Copy
Being able to require() an ES module removes the reason most packages shipped two builds. The dual package hazard is a layout problem, and it survived.
Frameworks
Your Reactive Graph Computed 4,11. That State Never Existed.
A single-pass push through a diamond recomputes the leaf twice, and the first result mixes a fresh value with a stale one. Two passes are what remove it.
Language internals
Your Conditional Type Answered Twice. Both Answers Are Right.
A naked type parameter splits its union before the conditional runs, so IsArray<string[] | number> comes back as 'no' | 'yes'. Read out of TypeScript 7.0.2.
Tooling and build
Vite 8 Ships One Bundler, Not One Pipeline
Vite 7 depends on esbuild and Rollup; Vite 8 on neither. Serving one module from both majors shows what the swap to Rolldown changed and what it left alone.
Sections
The pillars
- Language internals4 articles
- Runtime and performance4 articles
- Ecosystem and production3 articles
- Frameworks2 articles
- Tooling and build2 articles
Read in order
Series
- Series 01
The software supply chain
3 parts - Series 02
The V8 object model
3 parts - Series 03
Async machinery
2 parts - Series 04
Reactivity
2 parts - Series 05
The build pipeline
2 parts - Series 06
The TypeScript type system
2 parts