When I use the map function to make a copy of an array of objects, why doesn't it throw an error when adding a new property "xxx"? This new property "xxx" is not declared in the interface.
interface A{
a:number;
b:string;
};
let originalArray:A[] = [{a:1, b:"a"}, {a:2, b:"b"}];
let copiedArray:A[] = originalArray.map((item)=>({...item, xxx:"abc"}));
Since the variable b can still be assigned to variable a.
Let's look at the following example:
interface A {
a: number;
b: string;
};
interface B {
a: number;
b: string;
xxx: string;
}
declare var a: A[]
declare var b: B[]
a = b // ok
b = a // error
b has all the properties of a, making it safe to assign b to a.
However, it is not safe to assign a to b.
interface A {
a: number;
b: string;
};
interface B {
a: number;
b: string;
xxx: string;
}
let a:B[] = [{a:1, b:"a"}, {a:2, b:"b"}]; // error
This is because they are covariant.
If you are interested in contravariance, check out this example:
interface A {
a: number;
b: string;
};
interface B {
a: number;
b: string;
xxx: string;
}
class C<T>{
method = (a: T) => { }
}
let a: C<A> = new C()
let b: C<B> = new C()
// vice versa
a = b // error
b = a // ok
I am currently facing a challenge in my angular2 project where I need to import a 3rd party library. Here are the steps I have taken so far: ng new myproject npm install --save createjs-easeljs npm install @types/easeljs However, I am stuck at this poin ...
My unit tests are set up using Karma and Mocha. The reason I use Karma is because some of the functionality being tested requires a web browser, even if it's just a fake headless one. However, most of my code can be run in either a browser or Node.js. ...
Recently, I noticed that when using node JS with Angular-CLI, my .ts files are being transmitted to the client through HTTP. For example, accessing http://localhost/main.ts would deliver my main.ts file to the user. My understanding is that ts files are s ...
I'm currently facing an issue while compiling Typescript where the compiler is throwing an error: TypeError: myVariable is not a function at Object.<anonymous> (/home/anon/Desktop/Typescript/main.js:37:1) at Module._compile (internal/mo ...
I have successfully established a connection and written to my MongoDB collection, but I am encountering a type error that is causing some confusion. Below is the code snippet along with the error message: interface Movie { id: number; title: string; ...
I am experiencing an issue where certain HTML content does not load until the component has received data from an API call through a service. Below is the relevant code snippet: import { ApiService } from './services/api.service'; @Component({ ...
Struggling to find a solution for accessing nested object properties dynamically? The property path needs to be represented as an array of strings. For example, to retrieve the label, use ['type', 'label'] I'm at a roadblock wit ...
Below are my typescript functions. When I edit in vscode, the second function does not show any error message. However, upon compilation, an error is displayed for the second function: error TS2322: Type 'Promise<void>' is not assignable t ...
After building an angular application, I encountered a strange issue where it runs smoothly in non-production mode but throws an error when running with --prod: Uncaught TypeError: this._platformLocation.onPopState is not a function I have double-checked ...
if (window?.sessionStorage?.getItem('accessToken')?.length > 0) { this.navigateToApplication(); } Encountering the following error: Object is possibly 'undefined'.ts(2532) Any suggestions on how to resolve this issue? I am attem ...
Encountering a frustrating issue with multiple typescript errors while attempting to conditionally render the Next.js Link component or a button element. If the href prop is passed, the intention is to render the Next.js built-in Link component; otherwise, ...
In this particular scenario, the initial expression {{ bar }} remains static, whereas the subsequent expression {{ "" + bar }} undergoes updates: For example: two 1588950994873 The question arises: why does this differentiation exist? import { Com ...
Currently, I am working on developing my own Autocomplete component by utilizing the useAutocomplete hook from the mui/base package. Most parts of the implementation are functioning correctly, except for the disabled option. My expectation is that the com ...
I am currently utilizing the Playwright tool to carry out testing on an angular application. One particular scenario involves a modal that is displayed by default when a page is loaded. Despite my best efforts, I have been unable to successfully close this ...
Currently, in VSCode, the typescript compiler is at TypeScript React 4.4.2 and it's pointing to a TS(2339) error: Property 'Col' does not exist on type 'FC<GridProps>'. I have attempted to add this prop to GridProps: export ...
Seeking a way to incorporate the google diff/match/patch lib into an Angular application for displaying the variance between two texts. Here's how I plan on using it: public ContentHtml: SafeHtml; compare(text1: string, text2: string):void { var ...
During the installation of react-diagrams by projectStorm, I encountered some errors which are shown in the following image: errorImg Despite attempting to downgrade the version of '@emotion/core' to ^10.0.0, the issue persisted. Here is a view ...
I have encountered a strange issue while using Stripe webhooks to process payments on my website. When I set the currency to USD, it prompts me to provide an address outside of India, which is expected. However, when I change the currency to INR, the addre ...
One of the pages on my site contains tabs that are only loaded when clicked: explore.html <ion-tabs> <ion-tab [root]="tab1Root" [tabTitle]="hotTitle" tabIcon="flame"></ion-tab> <ion-tab [root]="tab2Root" [tabTitle]="searchTitle ...
Whenever a device loses internet connection, my app crashes due to an imported component that relies on Google Maps. To address this issue and prevent the app from showing a blank screen, I want to intercept the failed Google Maps import and display an err ...