Can a utility type be created to identify whether a type is a literal value? For example:
type IsLiteral<T> ...
type IsStringALiteral = IsLiteral<string> // false
type IsStringLiteralALiteral = IsLiteral<'abc'> // true
type IsStringALiteral = IsLiteral<bool> // false
type IsStringLiteralALiteral = IsLiteral<false> // true
Check out this article on determining if a type is a 'string' literal, 'number' literal, or 'string | number' literal: Determine if type is a 'string' literal, 'number' literal or 'string | number' literal
type IsStringLiteral<T> = string extends T ? true : false;
type T = {
true: true,
123: 123,
'text': 'text',
string: string,
}
type X = {[K in keyof T]: IsStringLiteral<T[K]>}
// type X = {
// true: false;
// 123: false;
// text: false;
// string: true;
// }
After some exploration, I've managed to solve the issue on my own:
type IsUnionCollection<T, U extends T = T> = T extends unknown ? ([U] extends [T] ? false : true) : false;
type IsStringText<A> = IsUnionCollection<A> extends true ? false : A extends string ? (string extends A ? false : true) : false;
type IsNumberValue<A> = IsUnionCollection<A> extends true ? false : A extends number ? (number extends A ? false : true) : false;
type IsBooleanValue<A> = IsUnionCollection<A> extends true ? false : A extends boolean ? (boolean extends A ? false : true) : false;
type IsLiteralValue<A> = IsStringText<A> extends true ? true : IsNumberValue<A> extends true ? true : IsBooleanValue<A> extends true ? true : false;
I incorporated IsUnionCollection functionality because I needed:
type IsStringUnionText = IsLiteralValue<'a' | 'b'> // false
If this doesn't meet your needs, here is an alternative approach:
type IsStringText<A> = A extends string ? (string extends A ? false : true) : false;
type IsNumberValue<A> = A extends number ? (number extends A ? false : true) : false;
type IsBooleanValue<A> = A extends boolean ? (boolean extends A ? false : true) : false;
type IsLiteralValue<A> = IsStringText<A> extends true ? true : IsNumberValue<A> extends true ? true : IsBooleanValue<A> extends true ? true : false;
If you're looking to differentiate between string types and literal types, this approach could be helpful:
type trueIfLiteral<T extends string> = string extends T ? false : true;
A literal type can be assigned to a string type, but not vice versa, which is why we use the constraint:
T extends string
Then we determine if a string is assignable to the type parameter:
string extends T ? false : true;
For more information, you can visit: Is it possible to get the value (not key) in a literal object as a literal, not its type (such as string) via mapped type in Typescript?
I have received a JSON result that looks like this: { "discipline":"ACLS", "course": [ { "value":"ACLS Initial", "classes":"0", "students":"0" }, { "BLS":"CPR Inst ...
Challenge Currently, I am developing a package that relies on decorators to initialize class object properties. The specific decorator is expected to set the name property of the class. // index.ts const Property = (_target: any, key: any) => { } cl ...
I have a Pinia + TypeScript store named user.ts with the following structure: import { User } from 'firebase/auth'; import { defineStore } from 'pinia'; export const useUserStore = defineStore('user', { state: () => ( ...
Help with mocking 'Request' in Mocha using express with Typescript needed! Here is the current approach: describe("Authorization middleware", () => { it("Fails when no authorization header", () => { const req = { ...
I'm facing a problem that I can't seem to solve because my knowledge of RxJs is limited. I've set up a file input for users to select an XLSX file (a spreadsheet) in order to import data into the database. Once the user confirms the file, v ...
concerts: [ { key: "field_concerts_time", lbl: "Date" }, { key: ["field_concert_fromtime", "field_concert_totime"], lbl: "Time", concat: "to" }, { key: "field_concerts_agereq", lbl: "Age R ...
My angular component requires a value that belongs to one of two lists. For example: @Input() public type!: enumA | enumB; However, this setup becomes problematic when the enums share values or are linked together in a way I find undesirable. I would pre ...
As I develop my website, I have incorporated an ngb-alert component to display an alert message to users upon login. While the alert itself is functioning properly, I have encountered an issue with the close button being misaligned, and I am struggling to ...
Can we transform this code snippet into something like the following? const array = ['a', 'b', 'c']; // this will change dynamically, may sometimes be ['a', 'e', 'f'] const readonlyArray = arr ...
I have an interface called MyInterface interface MyInterface { field1: boolean, field2: MyType, field3: MyType } In this interface, I want to create a new type that contains only the keys which have values of type MyType. While I know about the key ...
I have an array of data containing selected items, and I need to extract the IDs from this array into a new array so that I can send only the IDs to the back-end. Sample Code method toggleSelection(rows) { console.log('this.multipleSelection : &a ...
I am currently working on integrating mdx files into Next.js 13. After completing all necessary configurations in next.config and creating the file structure, I have the following path within the app folder: > docs > components > accordion > pa ...
Currently, I am conducting tests using Typescript to explore the feasibility of a project I have in mind. In one of my functions, I need to specify the type of 'this' as a class. While it technically works, I continue to encounter an error messag ...
When attempting to pass the result.nativeEvent.message to another function, I am encountering the error: Argument of type 'string' is not assignable to parameter of type '{ results: string; } on onUnityMessageController(result.nativeEvent.me ...
Understanding JQuery promises and deferred objects has been a bit of a challenge for me, so please bear with me. I should also mention that my application is built using React, Typescript, and ES6. Let's imagine we have an array of objects: [{ Objec ...
I am looking to customize the appearance of the select component by changing the background color to "grey", as well as adjusting the label and border colors from blue to a different color when clicking on the select box. Can anyone assist me with this? B ...
In my React-Typescript project, I recently set up i18next for multi-language support. Despite following the official documentation guidelines, I encountered compilation errors when running the app: Property 'changeLanguage' does not exist on type ...
Encountering an issue with Angular and Material for Angular - my application contains multiple modals that disable background scrolling when opened. However, there is one notification modal that should not block the background scroll. Despite not having a ...
As I was going through the TS Handbook, I stumbled upon mapped types where there's a code snippet demonstrating how to wrap an object property into a proxy. type Proxy<T> = { get(): T; set(value: T): void; } type Proxify<T> = { ...
Is there a way to iterate through the data I've subscribed to as an Observable, store it in an array, and then display the entire dataset from the array rather than just page by page? Currently, my code only shows data from each individual "page" but ...