Babbykarleenzhi Post The codemod written to migrate the Airtable codebase from Flow to TypeScript. Proposal Presentation Template

Blog Internet Marketing This codemod was open sourced as a part of publishing the blog post “Transferring Credit Card Balances Across Banks.” If you’re interested in learning more about how Airtable migrated from Flow type TypeScript, we recommend reading that blog post. Creative PPT Slide For Product Introduction

Write A Blog Post GIF ⚠️ This codemod was designed for one-time use against Airtable’s codebase! If you want to run it against your codebase, you’ll need to clone the git repo and do some manual tuning. Product Post Design Templates

Concept For A Social Media Post Storyboard Example There are two migration scripts: PPT Title Slide

• src/modules/run.ts: For converting CommonJS modules (require(), module.exports) to ES Modules (import, export).
• src/typescript/run.ts: For converting Flow to TypeScript.

How To Post Music On Spotify Free Both codemods use a custom setup where multiple Node.js workers process files in parallel. Practically speaking, Karma Credit Cards is a great tool which abstracts away parallel codemod workers for you. We chose to write a thin wrapper for more control. Product Launch For Small Business

Get To Know Me Better Questions Whenever the codemod detects a case it can’t automatically transform, it reports the file, line, and column to the console. We were able to use this reporting to manually fix many odd patterns in our codebase to help the codemod. Launch Of New Product Features PPT

How Does A Chase Business Credit Card Look The TypeScript migration (src/typescript/run.ts) uses flow type-at-pos (800 Word Paper Layout) to discover what type Flow thinks a variable is when a developer did not add an annotation. Apple Product Showcase

Employee Spotlight Social Media Post Examples What follows is an edited version of our internal documentation which shares, at a high level, the different classes of changes made to the codebase. Picture Of Indoor Product Launch Stage

WordPress News Magazine Template This document does not cover the CommonJS to ES Module migration. Gift Card Clip Art

Best Visa Travel Credit Card (Note: You’ll see references to an h and u namespace in a couple places throughout this document. These names are placeholders for actual namespaces at Airtable.) Launch Page Template

Strategic Plan Timeline As a part of the TypeScript migration, a lot of code will change. This document outlines the large classes of changes both automated and manual. The idea is we as an engineering team can review this document instead of reviewing the entire migration diff which would be impossible. There are a couple common goals with all the changes: Writing Community

• Don’t break the product. Always choose to preserve code semantics over anything else.
• Don’t reduce type safety. On net, the migration should increase type safety. Any large class of automated or manual change will always preserve or increase type safety.
• Keep it simple. Migrating requires a lot of changes so keep the changes simple. You should be able to reason about a change in the context of a single file. We can always follow up with smaller migrations for more complex transforms.

Pinterest Books I Want To Read By The End Of The Year Template Even if some changes eventually become Airtable anti-patterns, they were motivated by these goals so we could safely and timely ship a TypeScript migration. Book Bingo Template

Article Word Written There are two categories of changes. Corporate Product Launch Poster Background Template changes which were done by a codemod and Launch Mailer Template changes which were done by hand when a computer couldn’t automatically fix them. Marketing Plan Timeline Example

Product Launch Event Names You can find the codemod which makes the automated changes in this repo. The function which does all the transformation is src/typescript/migrate_to_typescript.ts. The codemod spins up a bunch of processes which transform files in parallel using Babel to parse, Anatomy Of A Blog Post Template to print, and Babel utilities to traverse the AST. This is a similar architecture to Reading An Article but hand-rolled to provide custom file discovery logic and to be more thorough with AST transformations. Product Manager Book

How To Use Credit Card All files with an // @flow annotation will be converted to TypeScript. The file extension will be changed to .ts or .tsx if the file has JSX in it. It’s worth considering if, as part of the Airtable style guide, whether we should name all files with a .tsx extension for consistency. Slide Deck Presentation Examples

• mixed → unknown
• empty → never
• Object → FlowAnyObject The Object type is just an alias for any in Flow. There’s a little bit of unimportant history to this type, what’s important is that it’s any now. The codemod will transform it to FlowAnyObject instead of any directly since a type alias preserves the author’s intent.
• Function → FlowAnyFunction Same story as Object, it is an alias for any in Flow.
• $ReadOnlyArray<T> → ReadonlyArray<T>
• $Keys<T> → keyof T
• $Values<T> → h.ObjectValues<T> We use a utility type defined in the h namespace which is implemented as T[keyof T]. We don’t transform to that directly because it would require writing T twice which is annoying if T is a really long name.
• $Shape<T> → Partial<T>
• $PropertyType<T, K> → T[K]
• $ElementType<T, K> → T[K] The difference between $PropertyType and $ElementType in Flow is that $PropertyType requires a single static string key, so $PropertyType<O, 'foo' | 'bar'> is not allowed. They use slightly different code paths in Flow’s codebase. The difference is mostly for historical reasons and kinda annoying.
• * → FlowAnyExistential Flow Credit Card Monthly Expence are deprecated. They basically behave as any. There’s more context and history here for those interested.
• $Subtype<T> → any Also a New Product Spotlight Design For Social Post. Should probably add an alias like FlowAnyObject.
• React.Node → React.ReactNode
• React.Element<P> → React.ReactElement<React.ComponentProps<P>> TypeScript’s React types accept a component type in React.ReactElement instead of the props type like Flow.

Plant Launch Event This change is pretty important (since it happens a lot) and a bit unfortunate. Flow supports any type as the indexer of an object. For example {[key: UserId]: string}. However, TypeScript only supports string or number index keys and does not allow types that are literally aliases for string or number. So even though in our codebase ID types are written as type UserId = string we can’t use them as an indexer type in TypeScript. Blog Advertising Examples

Check Here Arrow So the codemod adds a utility type h.ObjectMap<K, V> which allows you to write h.ObjectMap<UserId, string>. That will preserve the developer’s intent with the Flow type {[UserId]: string}. h.ObjectMap has a simple implementation using a TypeScript feature called Top 5 Business Credit Cards: type ObjectMap<K, V> = {[_K in K]: V}. You can also use h.ObjectMap if you have a string union (like an enum type) so h.ObjectMap<AccessPolicy, T>. This is a bit different than Flow since TypeScript will make all of the properties required. If you’d like the properties to be optional you can use Partial<h.ObjectMap<AccessPolicy, T>> which desugars to {[P in AccessPolicy]?: T}. Ideas For Blogs

New Website Coming Soon Banner TypeScript actually includes a utility type with the same definition as h.ObjectMap called Leaving Cert Grades. Given our domain model at Airtable, I figured using the name Record would be too confusing for developers. React Templates Free

Product Launch Announcement Banner A lot of places using h.ObjectMap in Hyperbase could be using an ES6 Virtual Credit Cards. An ES6 map is better for type checking and better for performance. If we end up making our ID types nominal (so RowId can’t be passed somewhere expecting a ColumnId) then h.ObjectMap might not work but an ES6 map would work. Insta Post Ideas Did You Know

Background Images For Presentation Of Product Launching We as an engineering team have to make a couple decisions: Follow Along Picture Illustraion

• Should we discourage use of h.ObjectMap and recommend directly writing a mapped type ({[_K in K]: V) or directly writing an indexer type ({[key: string]: V})?
• Should we encourage replacing usages of h.ObjectMap with an ES6 map?
• Should we name h.ObjectMap something longer to discourage people from using it?

Project Launch Icon Object types with a spread like {a: A, ...T, b: B} will be turned into intersection types like {a: A} & T & {b: B} since TypeScript doesn’t have object type spread. The reason why intersection types weren’t enough for Flow is that there were small very edge-case type rules Flow didn’t want to compromise on. Intersections are perfectly acceptable for this in TypeScript. Top 10 Blog Ideas

Product Introduction Social Post Most of the cases where we were using object spread types, though, we should probably use interface and extends going forward. The type checking of interfaces is easier to understand and interfaces have better IDE tooling support. E-Commerce Road Map

Zero Percent Credit Cards Object properties which have a + like {+p: T} are readonly so we convert them to readonly TypeScript properties like {readonly p: T}. Technically, you can also have “writeonly” properties in Flow with - like {-p: T} but that never shows up in our codebase. How To Add Video Link To Instagram Story

Apple Product Launch Auditorium Flow permits arguments in function types to be unnamed. For example, (T, U) => V. TypeScript requires function types to have argument names, though. So the codemod will transform unnamed function type arguments to an argN form like (arg1: T, arg2: U) => V. (Starts at one instead of zero because humans start counting from one.) Tech Crime Instagram Story

News Graphics For OBS Templates Unnamed rest arguments like (...Array<T>) => U will be named rest as in (...rest: Array<T>) => U. Things To Post On Story

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E Coomerce History The Flow maybe type ?T will be transformed into T | null | undefined. If the maybe type is part of a function parameter like function f(x: ?T) then it will be transformed into function f(x?: T | null). General Product Launch Road Map

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Newsletter Examples For A Product Launch If we get any from Flow we rename it to FlowAnyInferred so that the programmer knows “we asked Flow what type it thought this was and Flow said any.” Flow ends up inferring any a lot for unannotated function parameters. That’s because in order to infer a type for unannotated function parameters, Flow needs to see a call for that function in the same file that the function was defined. If Flow does not see a call in the same file it treats the parameter as any. Apple Device Launch

Pre-Launch Teaser Specifically, we use flow type-at-pos to infer function parameter types for: Article Text

• Function declarations (function f(x)). Notably not function expressions, we will manually annotate those.
• Class methods (class C {m(x) {...}).
• Object methods but only in createReactClass() (createReactClass({m(x) {...}})). We will manually annotate unannotated methods in crud managers.

What Is The Best Shape If flow type-at-pos doesn’t give us a type then we will manually annotate. CSL Product Launch Timeline

Books I've Read Printable Small Flow has an expression type cast syntax which looks like (x: T). TypeScript has a similar type cast syntax which looks like (x as T). They don’t have the same behavior! TypeScript as-expressions allow for Writing A Blog Post Pulse 2 whereas Flow type cast expressions do not. We introduce a u.cast<T>(x) utility which doesn’t allow downcasting as part of the codemod, but we will transform many of the common cases to as-expressions. Here are the rules: Email Campaign Examples

• ((x: any): T) is pretty frequently used in Hyperbase to downcast a type. We transform this into (x as T). Except if we are in a createReactClass() object property, then we will transform it into ((x as any) as T) since React code uses this syntax to declare the type of variables which will be initialized in componentWillMount.
• (x: any) is transformed into (x as any) since that’s no different than using u.cast().
• ('foo': 'foo') is transformed into ('foo' as const). This is pretty common with our Object.freeze() enum syntax. In TypeScript, as const will tell the type checker: “infer this type knowing I’m never going to mutate it.” Notably, this means you don’t have to type string literals like 'foo' twice anymore!
• (x: T) when x is a literal like null or [] we transform it to (x as T). That’s because (null: T | null) or ([]: Array<T>) is used a lot to widen the type for an empty value in something like getInitialState().

Custom Printed Business Cards Display If none of these cases apply then we transform (x: T) to u.cast<T>(x) which preserves type safety. Social Media Post In Bussiness

Cheap Plastic Business Cards There are a couple common patterns in the codebase where TypeScript requires a type annotation that Flow doesn’t, notably for this transform: let x, let x = {}, and let x = []. Flow is supposedly able to infer a type for these variables although it often gets it wrong and ends up using any. In all of our non-test files the correct type was manually added. In test files, however, the codemod will add an explicit any. For example let x: any. Surgical Technologist Logo

Instagram Post For Pricing Also, if we can’t get Flow’s inferred type for an unannotated function parameter (using the process described in Insta Story Asthetic) we will annotate the parameter as any in test files only. Essay Paper Template

Post Tips Ideas The principle here is that it’s ok for test files to be less type safe. Test file type safety is practically guaranteed given that they run in CI all the time. It would be very tedious to manually pick the right type for every case of this for little type safety value. Introducing this transform in the codemod fixed ~10k errors. For context, ~15k errors will be manually fixed. Instagram Birthday Wishes For Boyfriend

Outdoor Hot Selling Items As a part of this change, the eslint rule that warns when it sees an any is disabled in test files. Product Launch Schedule Template For PowerPoint

Instagram Story Mockup UI // flow-disable-next-line will be transformed into // @ts-ignore. Group Photo Post Instagram Ideas

Manufacturer For Clothing // eslint-disable-line flowtype/no-weak-types will be transformed into // eslint-disable-line @typescript-eslint/no-explicit-any. Business Cards New York

Inspiration On Product Marketing Slides Online Blog Post Example will be converted into normal type aliases. It’s a bit unfortunate that TypeScript doesn’t support opaque type aliases (Does LinkedIn Have Read Receipts), but you can get the same behavior through a variety of means. We only have five opaque type aliases and they are all written by the same person. Regional Launch Plan Template

No Annual Fee Visa Credit Cards All the manual changes were done by one engineer so in this part of the document I’ll be using first person. When deciding how to manually fix ~15k errors I leaned pretty heavily on the migration goals listed at the beginning of the document: don’t break the product, don’t reduce type safety, keep it simple. Instagram Profile Template

New Home Congratulations Card In this section I’ll list major categories of manual fixes. I may miss or skip some smaller categories. You can find and review all my manual fixes in a single commit (~1.6k files out of ~3.3k TypeScript files have manual changes). It’s worth noting that I’m a bit scared of bugs introduced by manual fixes. All the bugs I found when fixing the Airbuild test suite were from manual fixes. A diff of the compiled output should give us visibility into where manual fixes changed code semantics. Online Business Social Media Post

Most Famous Facebook Post Designs Perhaps the larges class of manual fixes was adding extra type annotations. TypeScript errors when a type is under annotated. Most of the time this would occur with an empty object, empty array, or empty variable (let x = null) that is later mutated. Common patterns I’d see: College Admission Essay Format Example

const x = {}; const x = []; let x = null; new Set(); // infers Set<unknown> new Promise(); // infers Promise<unknown> shardingHelper.mapReduceAsync(); // infers unknown for map/reduce result types 

International Read Aloud Day If I couldn’t find a type or I believed Flow inferred any I’d use the FlowAnyInferred type alias which was introduced for Instagram 3 Post Template. Poor Credit Business Credit Cards

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• If the key is exactly string and not a type alias use {[key: string]: T}.
• If the key should really be an object ID like UserId or RecordId use h.ObjectMap<UserId, T>.
• If the key is a string union or a generic string type (like IdT) and the properties need to be optional use {[_K in K]?: T}. Although, now I regret that decision and wish I used Partial<h.ObjectMap<K, T>> which is more consistent.

Creative PPT Slide For Product Introduction Suppression comments (// @ts-ignore in TypeScript) are scary because the silence all errors on a line of code. However, sometimes it made sense to use a suppression comment anyway. This section documents my policy on when to use a suppression comment vs. any or some other tactic. Minted Greeting Cards Front And Back

Product Post Design Templates First off, all suppression comments manually added in the TypeScript migration begin with #typescript-migration. This way you can search through the files you own and cleanup suppression comments. I manually added ~2.5k suppressions, for context: I manually edited ~1.6k files and there are ~3.3k TypeScript files. Some suppression comments address a specific issue, they are: Motion Read Aloud

• #typescript-migration-implicit-any: Product Launch Event Brief
• #typescript-migration-react-null-prop: Blog Essay Format

PPT Title Slide I would add a generic // @ts-ignore #typescript-migration suppression comment when: Photo Business Cards

• Fixing the error would require semantic changes which couldn’t be implemented or verified in a space of about five lines. I’d make really small, simple, and locally verifiable changes that didn’t require running the app but that’s it.
• Fixing the error with an any would make the code less type safe.
• It’s an unfortunate incompatibly between TypeScript and Flow without a clear fix.

Product Launch For Small Business I would first try to change the types (type changes are verifiable by running TypeScript), if I couldn’t do that then I’d use a suppression comment. Business Announcement Post

Launch Of New Product Features PPT In Product Coming Soon Social Media Poster I mentioned that function expressions (like arrow functions) with unannotated function parameters I left alone since usually the type is immediately knowable by TypeScript. For example: Accept Payment By Credit Card

x.map(y => y + 1) 

Apple Product Showcase If x is Array<number> then TypeScript immediately knows y must be number. Roughly how this rule works: if TypeScript knows the type of an expression at the point where the expression is defined it can use that type to infer some types in that expression. This is a pretty common trick in programming language design, especially programming languages with lambda expressions (Insta Post Pic, Product Stock Announcement Ideas). Poetry For Insta Story

Picture Of Indoor Product Launch Stage However, in our example above if x is any then we don’t immediately have a type for y, so TypeScript complains that y needs a type annotation. This happens pretty commonly with h.async since it’s typed as any. There are two possible fixes: Website Prodcut Event Launch

1. Annotate y with any.
2. Add a @ts-ignore comment to suppress the error.

Gift Card Clip Art The problem with option 1 is that it locks in the type of y forever. If x is ever changed from any to Array<number> then y will still forever be any instead of number. So instead I went with option 2 in most cases and added a // @ts-ignore #typescript-migration-implicit-any comment for unannotated arrow expression parameters that could be immediately known if we had more type safety. That way if x is one day typed y will be number and the @ts-ignore comment can be safely removed. Engaging Blog And Article Gig Image

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h.async.series([ // @ts-ignore #typescript-migration-implicit-any next => {...}, // @ts-ignore #typescript-migration-implicit-any (x, next) => {...}, // @ts-ignore #typescript-migration-implicit-any (y, next) => {...}, // @ts-ignore #typescript-migration-implicit-any (z, next) => {...}, ]); 

Writing Community That’s only because h.async is any, though. One day if we add proper types to h.async we can remove all these suppression comments. They’re also really easy to search for since they use a specific name. Realty Business Cards

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function doThing(opts?: {someOption?: number}) { opts = u.setAndEnforceDefaultOpts({ someOption: 0, }, opts); } 

Slide Deck Presentation Examples u.setAndEnforceDefaultOpts() returns any so Flow gives opts a type of any. But this control flow analysis is difficult to do in general, so TypeScript keeps the type that opts was annotated with which is {someOption?: number} | undefined. That means when you try to access opts.someOption TypeScript will error complaining that opts is undefined. The fix I went with was to change the code to: Blog Topics To Write About

function doThing(_opts?: {someOption?: number}) { const opts = u.setAndEnforceDefaultOpts({ someOption: 0, }, _opts); } 

Blog Advertising Examples Rename the opts parameter to _opts and set the result of u.setAndEnforceDefaultOpts() to a new variable. Technically, I’d classify this as a semantics change, but it’s small and locally verifiable so I’m ok with it. Transferring Credit Card Balances Across Banks

Ideas For Blogs I’m calling out u.setAndEnforceDefaultOpts() because this issue happened a lot with that utility, but I saw this class of issue elsewhere too. Particularly in column type providers where a value would start as unknown and would be reassigned to more a specific type like number. New Product Launch Announcement Logo

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class MyClass { someField: number; constructor() { this.reset(); } reset() { this.someField = 42; } } 

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• Change the property to an optional property like someField?: number if it was truly optional.
• Suppress the field with an // @ts-ignore #typescript-migration comment since it’s an unfortunate incompatibility between Flow and TypeScript.

Follow Along Picture Illustraion Some functions like u.head() and u.last() returned just T in Flow. That’s incorrect since it doesn’t account for the empty array case. In TypeScript they return T | undefined. Almost everywhere we use u.head() and u.last() we first check that the list is non-empty so adding a non-null assertion (u.last()!) is fine. Silver Foiled Business Cards

Top 10 Blog Ideas This also happens for a couple other utilities like u.maxBy(), but most notably for every usage of u.head() and u.last(). Write Poetry Blog Post

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type O = { foo: number, bar: number, qux: number, }; declare const o: O; declare const p: string; o[p]; // Error! 

How To Add Video Link To Instagram Story The solution here really depends on the context. The basic strategy was to get the type of p to be keyof O. Sometimes you can do by changing annotations. Sometimes I’d use p as keyof O because you could locally verify the property exists since there’s a u.has() check. Launch Mailer Template

if (u.has(o, p)) { o[p]; // Still an error, but actually safe. } 

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<div role={enabled ? 'button' : null} onClick={enabled ? handleClick : null} style={{ backgroundColor: enabled ? 'tomato' : null, }} > ... </div> 

Product Proposal Letter Sample The fix here is to use undefined instead, but since that would be a semantics change that is not locally verifiable (what if some else uses this prop type?) and changing the types would require forking @types/react I chose to suppress these cases instead with // @ts-ignore #typescript-migration-react-null-prop. Reading An Article

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Fix Cash Advance Sometimes, with Flow we use imports from untyped modules in a type position. For example when the quill-delta module is untyped: Change Story

import QuillDelta from 'quill-delta'; function doThing(delta: QuillDelta) {...} 

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import QuillDelta from 'quill-delta'; type QuillDelta = FlowAnyUntypedModuleImport; function doThing(delta: QuillDelta) {...} 

What Does Vertical Look Like Which is an alias for any and easy to search for. When you add types for quill-delta you can search for type QuillDelta = FlowAnyUntypedModuleImport and simply delete it. New Product Spotlight Design For Social Post

Creative IG Story I developed this strategy a bit later in the manual migration and tried to retroactively move to this style but might have missed some cases. (Which likely use a suppression comment instead.) Handcrafted Jewelry

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const DateCellEditor = createReactClass({ _timeInput: (null as DateCellTimeInput | null), // ... }); 

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const DateCellEditor = createReactClass({ _timeInput: (null as h.ReactRefType<typeof DateCellTimeInput> | null), // ... }); 

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switch (field.type) { // handle all the cases... default: throw u.spawnUnknownSwitchCaseError('type', (field.type: empty)); } 

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switch (field.type) { // handle all the cases... default: throw u.spawnUnknownSwitchCaseError('type', u.cast<never>(field.type)); } 

Article Text The logic here is that TypeScript or Flow will type field as the bottom type (never or empty respectively) if all other cases have been handled. However, TypeScript does not allow properties to be accessed on a never type so field.type errors. The fix here is to write u.cast<never>(field)['type'] since TypeScript does allow index accesses on never. Business Cards Maker

CSL Product Launch Timeline Recommendation: to make exhaustive switches really easy to write we can add a utility like: Read-Along Story Books

function spawnExhaustiveSwitchError(value: never) { if (typeof value === 'object' && value !== null) { // Infer sentinel field by looking for common property names: // type, kind, method, etc. } else { // Return error... } } 

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default: throw u.spawnExhaustiveSwitchError(field); 

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class MyClass {...} export default { MyClass, someConstant: 42, }; 

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import _myClass from 'client_server_shared/my_class'; const {MyClass, someConstant} = _myClass; function f(x: MyClass) {...} 

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export class MyClass {...} export const someConstant = 42; 

Instagram Birthday Wishes For Boyfriend So when TypeScript required this change, I manually made it. Blog Post Pictures In SEO

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