A Small Year for tsc, a Giant Year for TypeScript
Effective TypeScript: 83 Specific Ways to Improve Your TypeScript
Effective TypeScript
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Posts by Effective TypeScript
What TypeScript & Elixir Can Learn from each Other (Advent of Code 2024)
Every year I do the Advent of Code programming competition in a different language and (eventually) write about it. Last year I used Elixir, a functional programming languages with immutable data types based on the Erlang runtime. This post describes Elixir, and how it offers JS/TS developers a g...
Recommendation Update: ✂️ Use knip to detect dead code and types
TL;DR: ts-prune is in maintenance mode. Use knip to find dead code instead. It's great!
Item 74: Know How to Reconstruct Types at Runtime
A fundamental part of TypeScript's design is that TypeScript types are erased at runtime. There's no way to access them. But inevitably, you'll want to do just that. This comes up most often when you want to validate that user input matches a TypeScript type. Faced with this problem, TypeScript d...
Item 36: Use a Distinct Type for Special Values
It's tempting to use "", 0 or -1 as special values: an empty string might represent text that hasn't loaded yet, or -1 could stand in for a missing number. In TypeScript, this is almost always a bad idea. Special values need to be handled specially, and giving them a distinct type, such as null,...
Notes on TypeScript 5.6
We TypeScript developers are a lucky bunch. While some languages (Python, JavaScript) are released annually, every three years (C++) or even less, we get four new versions of TypeScript every year. TypeScript 5.6 was released on September 9th, 2024. Let's take a look.
TypeScript 5.5: A Blockbuster Release
We TypeScript developers are a lucky bunch. While some languages (Python, JavaScript) are released annually, every three years (C++) or even less, we get four new versions of TypeScript every year. TypeScript 5.5 was released on June 20th, 2024, and it was a real blockbuster. Let's take a look.
A keyof puzzle
Effective TypeScript is nearly 400 pages long, but I've received the most feedback by far on just one passage. It comes in Item 7: Think of Types as Sets of Values: keyof (A&B) = (keyof A) | (keyof B)keyof (A|B) = (keyof A) & (keyof B) If you can build an intuition for why these equations hold,...
A TypeScripter's Take on Zig (Advent of Code 2023)
What can Zig learn from TypeScript, and what can TypeScript learn from Zig?
The Making of a TypeScript Feature: Inferring Type Predicates
Over the past few months I became a TypeScript contributor and implemented a new feature, type predicate inference, that should be one of the headliners for TypeScript 5.5. This post tells the story of how that happened: why I wanted to contribute to TypeScript, the journey to implementing the fe...
Now Available: Effective TypeScript, Second Edition
Fully updated, thoroughly revised, now with 50% more book!
Flow Nodes: How Type Inference Is Implemented
If a variable gets a type but no one looks at it, does it really get a type at all? This post looks at how type inference is implemented in the TypeScript compiler. It's of some interest to anyone who uses TypeScript and is curious how it works, but it will be most relevant to developers who want...
The Hidden Side of Type Predicates
Type guards are a powerful tool for improving TypeScript's built-in control flow analysis. This post looks at when it's appropriate to use a type predicate, and in particular what it means when a type predicate returns false.
Effective TypeScript Talk at Etsy (Dec 2020)
Back in 2020 I gave a whole series of Effective TypeScript talks at companies that were interested in the language and the book. The talk that I gave at Etsy in December of 2020 was one of the most fun. It was recorded and is now available to watch. It's about an hour.
Don't Write Traditional Getter and Setter Methods in JavaScript and TypeScript
Getter and setter methods (getFoo, setFoo) are common in Java and considered a best practice. But they're a code smell that's best avoided in JavaScript and TypeScript because the problem they solve in Java does not exist in JS/TS. This post looks at what that problem is and how you can solve it...
Using infer to unpack nested types
TypeScript's infer keyword can infer quite a bit more than you might expect. It's extremely effective at extracting types from the sort of nested structures that you might get from codegen or an API specification.
Overload on the type of this to specialize generics (The Lost Item)
I cut one item from Effective TypeScript during the final stages of editing. Four years later, it's time for it to see the light of day! It's a trick for specializing generic types for certain subtypes of their type parameters. This post shows how it works, why it's indispensible for wrapper type...
The Saga of the Closure Compiler, and Why TypeScript Won
This post looks at the Closure Compiler, Google's tool from the mid-2000s for adding types to JavaScript. It looks at how its focus on minification led to very different design choices than TypeScript, and how this and a few other factors led to TypeScript becoming the ubiquitous solution for Jav...
TypeScript and SQL: Six Ways to Bridge the Divide
If you develop server code with TypeScript, you'll inevitably come up against the question of how to interact with your database. There's lots of type information in your database (the structure of the tables) and it's not immediately clear how to share that type information between the DB and Ty...
Notes on TypeScript 5.1
Every three months we get a new TypeScript release and TypeScript 5.1 landed on June 1, 2023. This release has a few interesting new features, but by far the most noticeable changes are performance improvements and error message ergonomics. Let's take a look!