Dan Vanderkam
@danvdk
Followers
3,256
Following
126
Media
94
Statuses
1,327
Independent software developer, formerly @sidewalklabs and Google. Author of Effective TypeScript, now in its 2nd edition (May 2024):
Hudson Valley, NY
Joined February 2009
Don't wanna be here?
Send us removal request.
Explore trending content on Musk Viewer
#enhypen
• 389433 Tweets
Liz Cheney
• 264874 Tweets
#ゴジラマイナスワン
• 171274 Tweets
Ruben Amorim
• 114642 Tweets
#OUROADCLOSEFRiEND2_EP9
• 67829 Tweets
#金曜ロードショー
• 62410 Tweets
taemin
• 47221 Tweets
#シェリン特番
• 45737 Tweets
REST IN PEACE SUARUKH KHAN
• 45390 Tweets
モンハン
• 28200 Tweets
Zomvivor 1st Look
• 26134 Tweets
雇用統計
• 26033 Tweets
MINQ BEACH DATE
• 24874 Tweets
山崎監督
• 22641 Tweets
ヴェノム
• 21764 Tweets
#ساعه_استجابه
• 19113 Tweets
#ライオンの隠れ家
• 17623 Tweets
#マリン船長のスペース
• 14750 Tweets
بندر
• 11944 Tweets
フリーダム強奪事件
• 11502 Tweets
敷島さん
• 10981 Tweets
Pinned Tweet
It's here! 🎉 The 2nd edition of Effective TypeScript is now available in all formats. The bird on the cover is the same, but the content is throughly revised and expanded to reflect how TS is used in 2024. Get your copy today!
@OReillyMedia
8
25
179
Another use of
@TypeScript
4.1's template literal types: extracting the URL parameters from an express route. Pretty amazing you can do this in the type system!
24
170
646
Put up my second
#TypeScript
PR! It allows the type checker to infer "type predicates" when a function returns a boolean that's tied to a refinement on one of its parameters. I have no idea if it'll be accepted, but I sure learned a lot implementing it!
8
22
243
New Effective
#TypeScript
blog post: a command to visualize what TypeScript is compiling using a treemap (the results may surprise you!). Or: how I found out I was compiling 80+ MB of types for Google APIs that I wasn't using.
1
28
171
I’m excited to launch
http://t.co/NFkT7kZRU1!
Browse 40,000 mapped historic photos of
#NYC
from the
@NYPL
http://t.co/eH0R9AsbWb
17
143
161
Recommendation update: use knip to find dead code, types and dependencies in your
@typescript
✂️
3
18
108
I wrote a book! Happy to announce that _Effective TypeScript: 62 Specific Ways to Improve Your TypeScript_ is now available for purchase. I learned a lot writing it and I hope you'll have the same experience reading it.
10
12
107
After using TypeScript for 8+ years, I had a mind-blowing realization: type inference is implemented completely backwards from how I think about it! Read on for the "missing manual" on Flow Nodes and TS type inference internals.
1
8
83
For my PR to infer type predicates, I needed to understand TypeScript's control flow graph. So I added a graph visualization to
@DavidSherret
's amazing TypeScript AST Viewer. It's live now and very fun to play with! Edges go backwards in execution order.
2
7
77
One of my goals this year was to become a TypeScript contributor. Over the past three months, I did just that! This post tells the story of how Type Predicate Inference came about and what I learned along the way.
3
8
59
Do you write about
@typescript
? These four words are my pet peeves. Please avoid them if you can!
8
9
55
Which of these would you rather show your users when they call a function in
@TypeScript
? As a library writer, you do have some control! Read more about the strange world of type display in the latest Effective TypeScript blog post:
1
4
40
A quibble with
@mattpocockuk
's excellent writeup : I'd call the "implicit index signature" for type a bug and a good reason to use interface instead because it can lead to unsoundness:
1
7
38
The Seven Sources of Unsoundness in
#TypeScript
(and what you can do about them) . Have one that's not on this list? Let me know and I'll add it!
6
16
34
My five most popular Effective
#TypeScript
posts of 2020: "Good use of generics or bad use of generics?" takes the top spot!
2
11
35
Very excited to see inferred type predicates headline TS 5.5! I hope everyone enjoys the bird-themed release notes 🦜
Announcing TypeScript 5.5 Beta! 📣
Now with type predicate inference, more type narrowing, an @import tag for JSDoc, the --isolatedDeclarations flag, performance & reliability improvements, and much more!
12
197
916
0
3
33
Use
@TypeScript
? Check out dtsearch, a tool search npm for just the packages that have types, whether bundled or on DefinitelyTyped. Thanks to
@orta
and
@haroenv
for all their help making this work!
1
7
30
Excited to get my copy of
@LearningTSBook
! Congrats
@JoshuaKGoldberg
! The cover looks great. Can you tell us more about your choice of the sun parakeet??
2
2
32
@mpocock1
Just remember that Object.keys has that signature for a reason: it’s unsound otherwise.
4
1
29
I put together a small library for type-safe express routes using
@typescript
4.1's new template literal types called crosswalk ("safe route", get it?). If you use Express and TypeScript, give it a try!
2
10
27
The Golden Rule of Generics in
@typescript
(probably other languages, too!) h/t to
@SeaRyanC
and the new TS handbook for this amazingly concrete rule.
2
6
25
Well this was exciting! File a
@TypeScript
bug. Don't expect anything to happen. Two days later… Anders has a PR to fix it!
1
1
24
Nice writeup of TypeScript's new ability to infer type predicates from
@mattpocockuk
. I'm 0% surprised that Matt beat me to writing a blog post about this :)
1
2
25
I put up my first
#TypeScript
PR today! 🎉 It fixes a pretty inconsequential and weird bug, but I learned a lot about how TS works internally by tracking it down and fixing it.
1
4
23
After a summer hiatus, I'm back to blogging about
@TypeScript
! Read up on Exclusive Or and the Optional never Trick:
0
3
22
A new way to test types: how eslint-plugin-expect-type makes writing so easy and fun that you'll actually _want_ to do it!
@JoshuaKGoldberg
0
8
21
Most of my
@typescript
bug reports are misunderstandings on my part, but this alternative never gets old!
1
1
21
@mattpocockuk
You and me both,
@mattpocockuk
! I learned a ton writing this PR and it’s been amazing to see the reaction to it getting merged. I guess I wasn’t the only one who’s been wanting this!
1
0
19
New Effective
#TypeScript
post: The Hidden Side of Type Guards. It's clear what it means when a type guard returns true. But what about when it returns false?
1
3
18
I just published “Testing Types: An Introduction to dtslint”
0
9
19
Excited to see that the new Flow Node Charts have at least one high-profile user. And may have even indirectly led to some TypeScript speedups! Visualizing something has a way of nudging you to make it better.
@DavidSherret
For my PR to infer type predicates, I needed to understand TypeScript's control flow graph. So I added a graph visualization to
@DavidSherret
's amazing TypeScript AST Viewer. It's live now and very fun to play with! Edges go backwards in execution order.
2
7
77
1
0
17
Sure, you don't use `any` in your
@typescript
, but are all the authors of
@types
packages equally careful? Who wants noThirdPartyAny?
2
0
16
The
@typescript
language is both coded and _designed_ in the open. You can keep up on their latest thinking through
@drosenwasser
's weekly "Design Notes" issues. Here's an RSS feed for them!
1
5
15
If you've ever wanted to find dead code (and dead types!) in your
@typescript
project, then
@ncthis
's ts-prune is exactly what you're looking for. Read about it here
2
2
15
Does anyone use
@typescript
twoslash as a test system? Basically I want to write the result of adding "// ^?" in code and have twoslash assert that what I wrote matches what it would show. I like that this would test how the types _display_ ala literate-ts
@orta
1
0
14
Four years ago, I cut one item from Effective
@TypeScript
during the final stages of editing. Now it finally sees the light of day as a blog post! I'm curious how widely-known this is and if it's useful beyond typing _.chain.
0
3
13
ts-mover is a small tool built using
@dsherret
's ts-morph. You write a list of
@typescript
file moves and renames and it makes them happen. I've been doing some large-scale reorganizing recently and this has really helped!
0
3
13
Today on danvk blog: extracting text from an image using the
@ocropus
library
http://t.co/CulGEMRx4b
(with pictures!)
http://t.co/4m1LJQZtBA
0
11
13
Last blog post in my OCR series: Training an Ocropus OCR model. Witness the triumph!
http://t.co/suu7JJnPzB
http://t.co/L6LjihooCT
0
11
11
Better late than never! Just posted a write-up on my impressions of using
@deno_land
and
@TypeScript
to complete the 2022 Advent of Code. Overall: some good, some bad, some TC-39 proposals I'd love to see approved.
0
0
13
👀 Searched on the
@TypeScript
type-challenges repo to see if anyone had filed a solution using the built-in Extract helper and… wait a minute, what? Memory works in funny ways!
1
0
12
@tannerlinsley
@TkDodo
@lukemorales
@typescript
The comment from
@TkDodo
is exactly right, TypeScript does refinement on the types of individual symbols. Once you split them apart, it can't keep track of the relationship any more. Doing this in general would be computationally hard. It can also be hard for people.
0
1
13
I'm impressed that this works! In
#TypeScript
2.1, you can pull a union of string literals tag type out of a tagged union type.
#MappedTypes
0
5
13
Hey
@TitianCernicova
@robpalmer2
was Bloomberg's "Dead Type Elimination" tool referenced in this post ever open sourced? Do you still use it? Is it too tied to Bloomberg's setup to be widely useful? I'm very curious about this topic!
1
1
13
Today's Effective TypeScript post looks at Google's Closure Compiler. What was it, how did it differ from
@TypeScript
and why was TS so much more widely adopted by the JS community?
2
5
12
I put together a small site for Effective TypeScript: . Subscribe via RSS or follow on Twitter to get sample items and TypeScript tips & tricks!
1
4
12
New Effective TypeScript blog post, in which I learn that "infer" can infer more than I knew!
0
1
11
What an amazing response to
http://t.co/NFkT7kZRU1.
Millions of image views and improved text transcriptions on nearly 6,000 photos!
@nypl
3
7
9
"strings that are actually numbers" wasn't a thing I ever expected
@TypeScript
's type system to accurately model. Kudos on the TS 4.4 beta! Now there's some things in my book that I need to rewrite… :)
TypeScript 4.4 Beta is ready to try!
We want your feedback on our new analyses, strictness flags, symbol/pattern indexers, --help menu revamp, perf improvements, and more, so read up on what's new and give it a shot!
6
164
548
3
1
11
If you want to learn
@TypeScript
through exercises and puzzles,
@mdevils
and
@antfu7
have you covered:
1
3
10
Excited to publicly announce the project I've been working on at Sidewalk Labs! In case any of the
@typescript
crowd were curious why there were so many Mapbox and GeoJSON examples in _Effective TypeScript_ :)
In an ideal world, developers, architects, and urban planners could explore endless options to design sustainable and affordable neighborhoods. But the traditional urban development process only produces a few options, leaving potentially better designs untapped.
3
13
74
0
0
10
My
#TSConf
2021 presentation is now on YouTube!
Delve into
@danvdk
's
#TSConf
presentation -
#TypeScript
Types: The First 500 Years. Learn type theory with some help from Michelangelo:
0
1
13
2
0
10
Another nice
http://t.co/NFkT7kZRU1
writeup today, this time from the New York Times!
http://t.co/47RQeAChnc
1
8
10
The
@typescript
4.1 RC breaks exactly one example in Effective TypeScript, in Item 23: Create Objects All at Once. The inferred type that "comes as a surprise" now does exactly what you'd intuitively expect!
2
1
10
Is this the simplest way to implement numeric addition in
@typescript
's type system? Pretty nice how it works with unions of numbers.
@JoshuaKGoldberg
2
3
10
Read about Unionize and Objectify, two
#TypeScript
helpers I've found extremely effective at simplifying problems with object types thanks to
@TitianCernicova
for introducing me to them!
2
2
10
Very excited to see type annotations coming to JS! “No build step” was always the Closure Compiler’s central dogma. Now we have a path to the same with
@typescript
. Nice work
@drosenwasser
and
@robpalmer2
! 🙌
1
2
9
TypeScript and SQL: Six Ways to Bridge the Divide. The video of my talk at TS Congress is up, along with a companion blog post. I have my favorite way to combine TypeScript and SQL. How do you like to do it?
1
1
9
The about the odyssey that led to jss, my new JSON manipulation command line tool:
0
5
9
@ddprrt
nice post on React children types! small nit: {} means anything but null/undefined, not any object. (It includes number and string.) Then ReactNode adds null | undefined, so it really is anything!
2
1
9
@sebastienlorber
@mattpocockuk
filter(Boolean) scares me because you almost always want to be checking for null/undefined, not 0. They're only equivalent for object types.
You can actually tell TS to only allow it in that situation by specializing on "this":
1
0
7
Glad you noticed! :)
Awesome talk by
@danvdk
at
#TSCongress
- nicely placed copy of "Effective TypeScript" in the background 😅♥️
0
0
16
0
0
9
@AdamRackis
I see you like Effective books! There’s also Effective TypeScript, now (as of this week) in its second edition:
3
0
9
TIL
@TypeScript
's mapped types work just as well on array and tuple types as they do on more typical object types:
1
1
8
Here's a roundup of the video, slides and tools from yesterday's
#PyCon2015
talk on Screenshot Tests & Visual Diffs:
http://t.co/HWOzTHeyej
0
1
8
Very excited to be speaking again at
#tsconf
!
You may remember them from
#TSConf
2019...it's Dan Vanderkam! Author of Effective TypeScript & Principal Software Engineer at
@sidewalklabs
, we can't wait to hear about the first 500 years of TypeScript Types at
#TSConf
2021! Welcome back
@danvdk
!
1
6
21
0
1
8
This has been on my list of most-desired TS features for years. I’m genuinely curious to see what breaks under —strictReadonly. In 2016 this felt too strict, but in 2024 it’s surprising we don’t have this.
1
0
6
Great talk
@TitianCernicova
! So satisfying to see those dependencies go away and your parallelism soar.
In his "Speeding up
#TypeScript
builds" presentation during
@ts_congress
today (11:55 AM EDT),
@TitianCernicova
will explore isolated declarations, a new feature of
@typescript
we've been working on in collaboration with
@Google
&
@Microsoft
0
3
6
0
2
8
When
@TypeScript
type inference goes wrong, you can often use a typed identity function to set it right. This post explores a few variations on this: h/t to
@bcherny
for teaching me about "tuple"!
0
5
8
@AdamRackis
@ThePrimeagen
@t3dotgg
Glad to hear you're a fan of the Effective series! This item is available free online. Here's they key quote: "Ideal TypeScript code includes type annotations for function/method signatures but not for the local variables created in their bodies."
1
1
8
I just published “A Typed pluck: exploring TypeScript 2.1’s mapped types”
0
4
6
TypeScript splits the atom! This post looks at
@typescript
4.1's template literal types, why they're a particularly "TypeScripty" construct, and what I think tasteful use of them will eventually look like.
0
1
7
New Effective
@TypeScript
blog post based on some hard-earned experience using the "Jsonify" generic and then deciding to remove it: The trouble with Jsonify: Unify types instead of modeling small differences
0
5
6
@mattpocockuk
I’m especially happy that TS team went with the simplest, most maximal version of this change. It’s not just for arrow functions. It’s not just for contextually-typed functions. It works for all functions. No special cases.
The clearest version, but also the scariest!
2
0
7
Funny enough, I got really into birding _after_ putting a bird on my book. The Oxpecker is a visual play on the cover of JavaScript: The Definitive Guide. Read the Colophon and see if you can figure it out!
1
0
7
Generics Tip
#2
: "Intersect what you have with whatever TypeScript wants"
It's like "as any" for
@TypeScript
generics but it doesn't break type inference
1
0
7
Tune in tomorrow for my Twitch debut! I’m a little nervous, but mostly just excited to talk
@typescript
and open source with
@JoshuaKGoldberg
📣 My Twitch open source coding stream resumes tomorrow!
@danvdk
and I will go over Dan's PR adding "twoslash" support to eslint-plugin-expect-type! 🙌
* What is twoslash?
* What is eslint-plugin-expect-type?
Find out tomorrow!
5
1
11
0
1
6
@mattpocockuk
The TypeScript playground is the best way to hammer this home. TypeScript on the left, JavaScript on the right.
2
0
6
Don’t Repeat Type Information in Documentation! This item from Effective
@TypeScript
has always been one of my favorites because it's so easy to apply its advice in code reviews. Now available as a free sample item:
1
0
6
Are
@typescript
project references a performance win if you use noEmit? e.g. for tsserver or ts-node or webpack. Curious to know before spending time on this. Context:
@sheetalkamat
3
2
6
@TAbrodi
@tannerlinsley
If what you really want is named (not positional) generics, you can improvise something using conditional types:
0
0
6
@yawaramin
@typescript
In practice TypeScript would infer the string literal for you. No repetition necessary. Here's a playground showing that in action:
1
0
6
Just launched, NCAA March Madness brackets on Google:
http://t.co/iHFC0ivnx4.
Super-proud of my team for putting this together!
4
10
6