Is it possible to conditionally narrow the type of object properties without causing an error when reassigning the whole object to another variable?
type A = {
prop: string | number;
}
type B = {
prop: string;
}
function f(a: A) {
if (typeof a.prop === 'string') {
let str: string = a.prop; // No error
let b: B = a; // Error
}
}
If you encounter this situation, consider using a type guard:
function IsPropertyString(a: A): a is B {
return typeof a.prop === "string"
}
function convertAtoB(a: A) {
if (IsPropertyString(a)) {
let strValue: string = a.prop; // No issues
let bObj: B = a; // No problems
}
}
When working with TypeScript, it's important to note that the type information defined in TypeScript is not accessible at runtime. This means that using the typeof operator may not give you the expected results, as it returns the JavaScript type instead of TypeScript's type information. To ensure the correct type is being used, alternative methods such as discriminator values, TypeScript classes, or type guards, like those seen in Tobias' solution, can be utilized.
Imagine you need to change the result of a function: (bob: Bob) => R => (bob: Bob) => R2 Is it possible to achieve this without changing the argument name? (e.g bob instead of using a general name like a) ...
Greetings to the TS community! Let's delve into a fascinating problem. Envision having a composition interface structured like this: type IWorker = { serviceTask: IServiceTask, serviceSomethingElse: IServiceColorPicker } type IServiceTask = { ...
I am utilizing sanity, and if you require more details, I will furnish it promptly. When I try to access http://localhost:3000/api/getComments, I encounter the following error message: ClientError: Unable to process value of "$tweetId=undefined". Kindly ...
So here's the scenario: I have an object of type 'any' and I want to assign it an object of type 'myResponse' as shown below. public obj: any; public set Result() { obj = myResponse; } Now, in another function ...
There seems to be an issue with the function not being called when passed into a functional component. While the onSubmit function is triggered, the login(email, password) function inside the Login component is never executed. Despite placing console.log s ...
Can anyone assist me with ng2 animate? I am looking to create a simple hover effect based on the code snippet below: @Component({ selector: 'category', template : require('./category.component.html'), styleUrls: ['./ca ...
In my TypeScript project, I am trying to concatenate the compiled output into a single file. I am using the SystemJs module, but I am facing an issue where the output changes when I include an 'import' statement in the script files. For example, ...
The SHA3 function allows for customizing the output length, as demonstrated in the code snippet below: var hash = CryptoJS.SHA3("Message", { outputLength: 512 }); var hash = CryptoJS.SHA3("Message", { outputLength: 384 }); var hash = CryptoJS.SHA3("Messag ...
I am implementing a unique set of types to enable angular form typing: import { FormArray, FormControl, FormGroup } from '@angular/forms'; export type DeepFormArray<T, U extends boolean | undefined = undefined> = T extends Array<any> ...
I am in the process of converting my current React app with JSX to TSX, but I am facing an issue with the AppContext not functioning as it did in my JSX version: App.TSX : export interface ContextType { cursor: {x: number, y: number}, } export const Ap ...
My search for Ionic 2 animations led me to some options, but none of them quite fit what I was looking for. I have a specific animation in mind - a "fade" effect between images. For example, I have a set of 5 images and I want each image to fade into the ...
It seems that many tsconfig.json examples include the compilerOptions section with entries like this: "module": "commonjs", "moduleResolution": "node" Setting both values to commonjs and node respectively may seem r ...
Despite importing DatepickerModule.forRoot() in my Angular unit test, I am encountering the following error: Error: Template parse errors: Can't bind to 'bsConfig' since it isn't a known property of 'input'. (" ...
English is not my first language, so please excuse any mistakes. I recently started learning Angular and I'm attempting to build a file upload button that lets users upload files based on dropdown menu options (such as USA States). Once uploaded, the ...
Below is the Dockerfile located in the root directory of my express server: FROM node:18 WORKDIR /usr/src/server COPY package*.json ./ RUN npm install COPY . . EXPOSE 3000 RUN npm run build CMD ["npm", "start"] Here is the contents of my .dockerign ...
My form consists of several fields and a switch component that toggles the visibility of certain parts of the form, as shown below: <Field name="field1" value={value1} /> <Field name="field2" value={value2} /> &l ...
When working with Java, I often use lombok to exclude certain fields from being printed. For instance, the @ToString.Exclude annotation can be used to prevent printing the user token. import lombok.ToString; public class TokenResponse { @ToString.Excl ...
When I attempted to run the below component, I encountered a type issue in my declaration. Here is the specific problem I am facing: Type '{ First: string[]; Second: string[]; Third: string[]; Four: string[]; }' is missing properties such as len ...
My package.json file includes: { "name": "projName", "version": "0.0.0", "scripts": { "ng": "ng", "prestart": "node aspnetcore-https", ... Upon running ...
The word controller is showing a red underline when I use import controller from '../controllers/test.controller'; In my typescript rest api application, the structure looks like this... project structure I am puzzled by the red line under cont ...