Conditional Types to the rescue: interface Circle { type: “circle”; radius: number; } interface Square { type: “square”; length: number; } type TypeName = “circle” | “square”; type ObjectType<T> = T extends “circle” ? Circle : T extends “square” ? Square : never; const shapes: (Circle | Square)[] = [ { type: “circle”, radius: 1 … Read more
No, this is not possible in TypeScript as of TS4.1. There are two issues I see; one might be overcome with a change to the TypeScript standard library typings for Array.prototype.map(), but the other would require a fairly large change to the type system to work in general and cannot currently be handled in a … Read more
I think this was caused by the extension called JavaScript and TypeScript Nightly. This was causing the syntax highlighting for .js and .ts files (.jsx and .tsx too). This was more of a bug with the latest version (currently 1.73.1). You can disable the extension to enable the syntax highlighting. This extension has now been … Read more
I’m going to show you a simple way: @Injectable() export class ProfileService { private profileObs$: BehaviorSubject<Profile> = new BehaviorSubject(null); getProfileObs(): Observable<Profile> { return this.profileObs$.asObservable(); } setProfileObs(profile: Profile) { this.profileObs$.next(profile); } } Now when you update something anywhere in the application, you can set that change by the ProfileService and each subscriber is receiving the change. … Read more
When including 3rd party libraries, there are two parts… the javascript code you want to execute, and the definition files to give the IDE all it’s strongly-typed goodness. Obviously, the first must be present if the app is to function. The easiest way to get that is to include the 3rd party library with a … Read more
Let’s assume valid code means : is syntactically correct with respect to the language specifications. Then the answer is YES. It is written down in the TypeScript Specifications (second paragraph) : TypeScript is a syntactic sugar for JavaScript. TypeScript syntax is a superset of ECMAScript 2015 (ES2015)syntax. Every JavaScript program is also a TypeScript program. … Read more
@Gunter is absolutely correct. The only thing I would like to add is actually how to deserialize json object keeping its date properties as dates and not strings (from the referenced post its not that easy to see this approach). Here is my attempt: export class Helper { public static Deserialize(data: string): any { return … Read more
The short answer is because arrow function is recreated every time, which will hurt the performance. This is a common misconception. The arrow function is recreated every time either way (although with useCallback subsequent ones may be thrown away immediately). What useCallback does is make it possible for the child component you use the callback … Read more
These steps resolved my issue: Step 1: Run this command: npm i localstorage-polyfill –save Step 2: Add these two lines in server.ts file: import ‘localstorage-polyfill’ global[‘localStorage’] = localStorage; Once you are done, run build command (eg: npm run build:serverless) All set now. Start the server again and you can see the issue is resolved. Note: … Read more
This is doable in TypeScript 2.0+. By using an inline { new(): T } type to capture this, you’ll get what you wanted: type Constructor<T> = { new (): T } class BaseModel { static getAll<T>(this: Constructor<T>): T[] { return [] // dummy impl } /** * Example of static method with an argument: */ … Read more