Is it true that Typescript removes any type or interface at compile time? If so, how is it possible to determine an object's primitive type using the typeof keyword? Are custom interfaces handled differently than primitive types?
const a = "string";
const b = 123;
const c = {};
const d = undefined
console.log(typeof a) -> 'string'
console.log(typeof b) -> 'number'
console.log(typeof c) -> 'Object'
console.log(typeof d) -> 'undefined'
typeof is a key operator in JavaScript.
In Typescript, the language leverages JS operators like typeof to facilitate tasks such as narrowing types during compilation.
For example:
declare const foo: string | number | Function | boolean
function bar() {
switch (typeof (foo)) {
case "string":
return foo.toLowerCase()
case "number":
return foo.toExponential()
case "boolean":
return foo
default:
return foo()
}
}
TS does not perform runtime validations.
The confusion may arise from the fact that typeof is a built-in operator in JS.
There are instances where I find myself needing to perform type checks on variables within a function before proceeding further. Personally, I try to minimize nesting in my code and often utilize early-return statements to keep the main functionality of a ...
Exploring firebase functions has been a fun journey for me. Everything works smoothly when I deploy to the firebase server using the command firebase deploy --only functions. However, I wanted to test my functions locally before deploying them, and encount ...
Is there a method for dynamically loading URLs in the templateUrl property? Similar to the code snippet below: @Component({ moduleId: module.id, selector: 'my-app', templateUrl: DynamicUrl, // Load DynamicUrl here styleUrls: [&ap ...
I've encountered an issue with types while working with dc.js version 4.2.7. To address this, I went ahead and installed what I believe to be the standard types module for dc.js using the following command: Command I used for Installation npm i @type ...
Currently, I am dealing with a JavaScript legacy project that utilizes the React framework. Within this project, there are React components defined which I wish to reuse in a completely different TypeScript React project. The JavaScript React component is ...
In my rollup.config.js file, I have only one output entry defined as follows: export default { input: './src/Index.tsx', output: { dir: './myBundle/bundle', format: 'iife', sourcemap: true, }, plugins: [ ...
Currently, I am faced with an issue while working on a typescript and sequelize project within an express application. The problem arises when trying to create a type-safe interface for utilizing the associate function. Within my Instance interface, there ...
When I log the items array in my props, it contains items. However, when I try to add to the array using .concat, I encounter an error stating Cannot read property 'concat' of undefined export default (props) => { const { items } = props; ...
Is there a way to retrieve all values of an Enum (specified as a parameter or generic) and return them in a list? Additionally, if the user has a specific role, I only need to retrieve certain Enum values provided as a parameter. I had the idea of groupin ...
Forgive me for asking a basic question, as I am not the most proficient frontend developer and have searched extensively online. Whenever I inspect my frontend application in Chrome, I keep encountering this error. (3) Material-UI: The component prop pro ...
As I develop classes to handle linear algebra operations on small constant size vectors and matrices, I encountered a scenario where the element casting behavior was not as expected. Consider the following code snippet: MyMathVector<int, 3> a ={1, 2 ...
As a beginner in TypeScript, I am looking to declare a type for an array object similar to the example below. const temp = [{ id: 0, // number follower_id: 0, // number followee_id: 0, // number created_at: '', // string delete_at: &ap ...
After trying to launch my Angular 5 page in the browser, I encountered an error message in the console. ERROR Error: StaticInjectorError(AppModule)[AppComponent -> MatDialog]: StaticInjectorError(Platform: core)[AppComponent -> MatDialog]: ...
Can someone help me rewrite the combination of *ngIF and *ngFor below? I understand that my issue may be similar to others, but please know that this is different. Everything seems to be working fine. The only problem I'm facing is that the color of ...
Currently, I am working with ngbdatepicker in Bootstrap. I have added a datepicker selector to appcomponent.html and the datepicker is showing up. Now, I need to retrieve that model value into the controller so that I can pass it to the parent appcomponent ...
Struggling with the syntax to properly map my incoming data in a static method. The structure of my json Array is as follows: [ { "documents": [ { "title": "+1 (film)", "is-saved": false, ...
It all began when the command tsc --init refused to work... I'm curious, what sets apart these three commands: npm install -g typescript npm install -g tsc npm install -g ntsc Initially, I assumed "tsc" was just an abbreviation for typescript, but ...
My challenge involves a state object and an update object that will merge with the state object. However, if the update value is null, it should be deleted instead of just combining them using {...a, ...b}. const obj = { other: new Date(), num: 5, ...
I have a requirement to display different screens in my Angular application based on the URL pasted by the user in the browser: http://localhost/screen1 (should show screen1) http://localhost/screen2 (should show screen2) To achieve this, I have set up ...
Currently working on an app with Ionic2 and facing a challenge with retrieving the player id after a user subscribes in order to store it in my database. Any suggestions on how I can retrieve the unique player id of OneSignal users post-subscription? ...