Yes you can handle with the catch operator like this and show alert as you want but firstly you have to import Rxjs for the same like this way import {Observable} from ‘rxjs/Rx’; return this.http.request(new Request(this.requestoptions)) .map((res: Response) => { if (res) { if (res.status === 201) { return [{ status: res.status, json: res }] … Read more
If you don’t provide a type Data (which must extend DataType), it will default to DataType. From previous release notes Consider a function that creates a new HTMLElement, calling it with no arguments generates a Div; you can optionally pass a list of children as well. Previously you would have to define it as: declare … Read more
You can use a const assertion: [‘List’, ‘Of’, ‘Names’] .map((name, index) => [name, index % 2] as const) // insert `as const` here .map(([name, num]) => { }); // name: string, num: number Take a look at the playground sample.
You can simply create a new type, say, DeepPartial, which basically references itself (updated Jan 2022 to handle possible non-objects): type DeepPartial<T> = T extends object ? { [P in keyof T]?: DeepPartial<T[P]>; } : T; Then, you can use it as such: const foobar: DeepPartial<Foobar> = { foo: 1, bar: { baz: true } … 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
A feature request for allowing you to just check array.length > 0 to guard against empty arrays, microsoft/TypeScript#38000, was declined as being too complex. Essentially you cannot usually simply check length in TypeScript to convince the compiler about the availability of properties at given numeric keys. You can define a non-empty array type like this: … Read more
Private keyword The private keyword in TypeScript is a compile time annotation. It tells the compiler that a property should only be accessible inside that class: class PrivateKeywordClass { private value = 1; } const obj = new PrivateKeywordClass(); obj.value // compiler error: Property ‘value’ is private and only accessible within class ‘PrivateKeywordClass’. However compile … Read more
Let’s say you’re developing a package “A” that have @types/some-module package in devDependencies. For some reason you’re exporting the type from @types/some-module: import { SomeType } from ‘some-module’; export default class APackageClass { constructor(private config: SomeType) { // … } } Right now TypeScript consumers of package “A” are unable to guess what SomeType is, … Read more
There is no compiler flag to make the compiler behave in a nominal way, indeed there in principle can’t be such a flag as that would break a lot of javascript scenarios. There are several techniques generally used to emulate some kind of nominal typing. Branded types are usually used for primitives (pick one from … Read more
I believe this is a consequence of the distributive property of conditional types in Typescript. Essentially, (S | T) extends A ? B : C is equivalent to (S extends A ? B : C) | (T extends A ? B : C), i.e. the conditional type distributes over the union in the extends clause. … Read more