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Pinterest’s 3.7M-line TypeScript migration 📄, OpenAI Codex 📜, Astro 5.7 🚀

TLDR Web Dev <dan@tldrnewsletter.com>

April 17, 11:18 am

TLDR WebDev
Pinterest successfully migrated 3.7 million lines of code from Flow to TypeScript over eight months. The migration used a "big bang" approach ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌  ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ 

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Articles & Tutorials

Migrating 3.7 Million Lines of Flow Code to TypeScript (10 minute read)

Pinterest successfully migrated 3.7 million lines of code from Flow to TypeScript over eight months. The migration used a "big bang" approach using codemods and had three phases: setup, conversion, and integration. Pinterest validated the migration through detailed testing, including daily automated tests, manual testing, and byte-for-byte comparisons of transpiled JavaScript.
Memoizing components in React: a case for useMemo (10 minute read)

`useMemo` is often a better choice than `React.memo` for optimizing component rendering in React. `useMemo` provides more explicit dependency tracking, makes optimizations visible at the usage site, and has granular control.
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Opinions & Advice

AI tools are ironically way more useful for experienced devs than novices (Reddit Thread)

AI tools are the most useful for experienced devs as a force multiplier. Experienced devs with AI can learn new concepts quicker and overcome knowledge gaps faster, allowing them to work faster with less errors.
You're Probably Breaking the Llama Community License (10 minute read)

Many users and distributors of Meta's Llama models are likely violating the Llama Community License. These violations include failing to prominently display "Built with Llama" on related products/services and not including "Llama" at the beginning of fine-tuned model names.
🚀

Launches & Tools

Codex (GitHub Repo)

The OpenAI Codex CLI is an experimental, open-source coding agent for devs who work in the terminal. It provides ChatGPT-like reasoning with the ability to run code and manipulate files.
Introducing OpenAI o3 and o4-mini (20 minute read)

OpenAI has new models, o3 and o4-mini, that are more intelligent and efficient than previous versions like o1 and o3-mini. These models also have improved safety features, including a rebuilt safety training data and system-level mitigations.
Astro 5.7 (8 minute read)

Astro 5.7 has been released. The Experimental Fonts API allows for easy integration and optimization of fonts from various providers. The stable Sessions API allows for secure server-side storage of user data, supporting type-safety and cookie-less options with various storage drivers. SVG components are now natively supported, allowing direct import and use of SVG files as components within Astro projects.
🎁

Miscellaneous

Tract Postmortem (45 minute read)

Tract was a UK startup trying to address the housing crisis by improving the planning permission process. It explored various business models, including site sourcing, land appraisal, land promotion, and an AI-powered planning document editor, but struggled with a conservative market, complex land promotion, and low willingness to pay. The founders concluded that the British market's limitations made venture-backed disruption difficult and decided to shut down the company and return capital to investors.
OpenAI in talks to pay about $3 billion to acquire AI coding startup Windsurf (3 minute read)

OpenAI is reportedly in discussions to acquire Windsurf, an AI-powered code editor with a VSCode extension, for around $3 billion. Windsurf, a competitor to other AI coding tools like Cursor and offerings from Microsoft and Anthropic, is VC-backed and was recently valued at $2.85 billion.
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Quick Links

Plandex (GitHub Repo)

Plandex is an open-source, terminal-based AI coding agent designed for large, real-world projects with features like smart context management, configurable autonomy, and multi-provider model integration.
TLS Certificate Lifetimes Will Officially Reduce to 47 Days (5 minute read)

The CA/Browser Forum has voted to gradually reduce the maximum lifetime of TLS certificates to 47 days by March 15, 2029.
Herb (Website)

Herb is an HTML-aware Embedded Ruby parsing tool built on Prism, Ruby's official parser.

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