Questions tagged [typescript3.0]
Tag for questions specific to new features in TypeScript 3.x. For general TypeScript questions, the correct tag is TypeScript.
typescript3.0
166
questions
803
votes
11
answers
297k
views
'unknown' vs. 'any'
TypeScript 3.0 introduces unknown type, according to their wiki:
unknown is now a reserved type name, as it is now a built-in type.
Depending on your intended use of unknown, you may want to ...
- 8,646
115
votes
4
answers
79k
views
How to define string literal union type from constants in Typescript
I know I can define string union types to restrict variables to one of the possible string values:
type MyType = 'first' | 'second'
let myVar:MyType = 'first'
I need to construct a type like that ...
- 34.4k
61
votes
3
answers
57k
views
vscode typescript: 'Add all missing imports' shortcut
I am working on a typescript project (typescript3.x).
I recently noticed the Add all missing imports when I click on the bulb which comes when I am using more than one types which are not yet ...
- 1,610
57
votes
7
answers
15k
views
TypeScript const assertions: how to use Array.prototype.includes?
I am trying to use an array of elements as union type, something that became easy with const assertions in TS 3.4, so I can do this:
const CAPITAL_LETTERS = ['A', 'B', 'C', ..., 'Z'] as const;
type ...
- 1,876
41
votes
1
answer
12k
views
How do I get the return type of a class method in TypeScript
In newer TypeScript versions (I think 2.8 onwards?), I can easily obtain the return type of a function:
function f() { return "hi"; }
type MyType = ReturnType<typeof f>; //MyType is string
But ...
- 22.6k
37
votes
3
answers
108k
views
Typescript 3 Angular 7 StopPropagation and PreventDefault not working
I have a text input inside a div. Clicking on the input should set it to focus and stop the bubbling of the div click event. I've tried the stopPropagation and preventDefault on the text input event ...
- 2,168
37
votes
2
answers
41k
views
Do I ever need explicit allowSyntheticDefaultImports if esModuleInterop is true configuring TypeScript transpilation?
I need confirmation on the following theory. According to TS docs, there are two options that can be set in tsconfig.json.
--allowSyntheticDefaultImports: Allow default imports from modules with no ...
- 37.9k
33
votes
6
answers
35k
views
cannot find name 'require' in angular 7(typescript 3.1.3)
My question is why this error shown?
ERROR in src/app/p2p/p2p.component.ts(14,16): error TS2580: Cannot
find name 'require'. Do you need to install type definitions for node?
Try npm i @types/...
- 441
31
votes
2
answers
20k
views
How to 'map' a Tuple to another Tuple type in Typescript 3.0
I have tuple of Maybe types:
class Maybe<T>{ }
type MaybeTuple = [Maybe<string>, Maybe<number>, Maybe<boolean>];
and I want to turn this into a tuple of types:
type ...
- 4,445
31
votes
3
answers
45k
views
How to clean typescript cache?
I don't know where to look at, and typescript answer here said that it is not cached
But it clearly cached the files. because this is my import
And yet, it cannot import the file from old path.
I ...
- 1,997
29
votes
3
answers
120k
views
Error: Type 'void' is not assignable to type 'ReactNode'
I'm getting an error while calling the function, this is just for practice so I have kept everything inside App.tsx. My class looks like this:
enum Actor {
None = '',
}
const initializeCard = () =&...
- 541
25
votes
3
answers
34k
views
TypeScript 3.x: Access properties of type unknown
I read from the TypeScript documentation, that you can't access properties from the type unknown:
// No property accesses, element accesses, or function calls
function f11(x: unknown) {
x.foo; /...
- 1,546
24
votes
2
answers
9k
views
Preventing inappropriate imports and enforcing project hierarchy in Typescript
In a TS project I'd like the following to be blocked:
A file from folder common importing from folder projectA
A file from folder projectB importing from folder projectA
I'd like the following to be ...
- 25.8k
18
votes
5
answers
12k
views
Generic curry function with TypeScript 3
TypeScript 3.0 introduced generic rest parameters.
Up until this point, curry functions had to be annotated in TypeScript with a finite number of function overloads and a series of conditional ...
- 920
14
votes
3
answers
9k
views
TypeScript: generically infer union type member based on a string literal property
TypeScript (v3.2.2) allows me to define a union of interfaces, each with a unique string literal property which can be used as a type guard, e.g.
type Device = Laptop | Desktop | Phone;
interface ...
- 1,271
14
votes
3
answers
14k
views
Typescript: Use `enum` values as `type`
I would like to use following enum's values:
export enum GenFormats {
SHORT_LOWER = 'm/f', SHORT_UPPER = 'M/F', FULL = 'Male/Female'
};
as type given below:
export interface IGenderOptions {
...
- 622
11
votes
1
answer
15k
views
How to use yield in Typescript classes
I am fresher to Typescript, while learning from the site, I got to know that yield can be used for Asynchronous Iteration using for-await-of. The below is the function in Javascript. Please help me ...
- 969
11
votes
3
answers
1k
views
Is it possible to Exclude an empty object from a union?
I have a union of two types, one of which is an empty obj.
type U = {} | { a: number } // | { b: string } | { c: boolean } ....
I would like to exclude the empty object from the union however ...
- 4,379
10
votes
1
answer
5k
views
"Cannot find module" error when using TypeScript 3 Project References
I'm trying to get TypeScript 3's project references working but struggling to import a function from a referenced project.
I have a ProjectA that references Shared. Here's the file structure:
...
- 4,623
10
votes
1
answer
4k
views
Sharing code between TypeScript projects (with React)?
This question: "Cannot find module" error when using TypeScript 3 Project References was somewhat helpful.
So was this one: Project references in TypeScript 3 with separate `outDir`
But I ...
- 183
9
votes
2
answers
15k
views
How to represent nested array with typescript
Say I have an array of strings like:
const a = ['foo', ['aa'], [['zzz',['bar']]]];
export const acceptsArray = (v: Array<any>) : string => {
returns flattenDeep(v).join(' ');
};
...
- 97.2k
9
votes
2
answers
7k
views
TS2538: Type 'unique symbol' cannot be used as an index type
I have this:
const symbols = {
typeMap: Symbol('type.map')
}
interface LangMap {
[key: string]: string | true,
golang: string,
typescript: string,
java: string,
swift: string
}
export ...
- 97.2k
8
votes
4
answers
3k
views
Migrate Node.js project to TypeScript from plain ES6
Is started migrating a Node.js project from plain ES6 to TypeScript.
What I did:
npm install -g typescript
npm install @types/node --save-dev
Setup tsconfig.json:
{
"compilerOptions": {
...
- 12.8k
8
votes
1
answer
4k
views
TypeScript path mapping "Cannot find module a-mapped/a"
I have a project with the following structure:
┌ tsconfig.json
│ {
│ "compilerOptions": {
│ "baseUrl": ".",
│ "paths": { "a-mapped/*": ["a/*"] }
│ }
│ }
│
├ a
│ └─ a.ts
│ export const ...
- 62.7k
8
votes
1
answer
775
views
Force object to have at least one key ( Object.keys(o).length > 0 )
Say I have this object
export interface Name {
[key: string]: boolean
}
const v = <Name>{};
how do I prevent this from compiling? What I want to do is force v to have at least one property:...
user7898461
7
votes
1
answer
8k
views
typescript remove optional property
I'm trying to build a dynamic type for a builder
export type Builder<T, K extends keyof T> = {
[P in K]: (value: T[P]) => Builder<T, K>;
} & {
build(): Readonly<T>;
};...
- 3,365
7
votes
1
answer
10k
views
Why can't I use StyleProp<ViewStyle> on my own component
I'm using TypeScript/Vscode for coding my React Native app. I want code completion on my custom components for style just like React Native's own View component does.
style prop View is defined like ...
- 34.4k
7
votes
2
answers
18k
views
Type 'T' is not assignable to type 'string'
Here is the problem : I wanted to make a function that gets a parameter and returns the same type.
I made the simpliest example possible :
type Test = <T>(arg: T) => T;
const test: Test = (...
- 825
7
votes
1
answer
2k
views
In TypeScript, is there a way to restrict extra/excess properties for a Partial<T> type when the type is a parameter to a function?
Is there a standard way to get Scenario 1 to have a compile error for not specifying known properties, just like in Scenario 2? Or is there some workaround?
class Class2 {
g: number;
}
class ...
- 1,612
7
votes
1
answer
1k
views
Compile single .ts file to stdout
I am looking to compile a single .ts file to stdout, something like this:
tsc foo.ts > foo.js
is this possible somehow? I want to control where the output goes without using a tsconfig.json file.
- 97.2k
6
votes
1
answer
12k
views
Generics for Arrays in TypeScript 3.0
So I see that 3.0 comes with generic typings for rest parameters so you can do something like this:
static identity<T extends any[]>(...values: T): T;
Is it possible to get something similar ...
- 4,413
6
votes
3
answers
10k
views
Typescript callback arguments, which are resolved using a function
I have a situation, where I call a function with some arguments, which are resolved using another function.
This is how the code looks.
function getArgs (): [string, number] {
return ['hello world'...
- 3,937
6
votes
2
answers
13k
views
TypeScript infer return type from used arguments
I'm not sure if this has been asked under different terminology. I've got a function that takes two arguments, where both can (independently) be a number, string, or undefined. The returned value is ...
- 34.4k
6
votes
2
answers
2k
views
Performance issue with @angular/material autocomplete
I am using Angular/Material Autocomplete. While loading data to the Autocomplete getting serious performance issues,like the rendering takes around 30 seconds and it takes more than 10 seconds to ...
- 2,386
5
votes
2
answers
3k
views
difference between `unknown` and `void`
According to this answer:
Using void instead means that forEach promises not to use the return value, so it can be called with a callback that returns any value
According to the TypeScript 3.0 ...
- 733
5
votes
1
answer
12k
views
Using generic type with class - type T does not satisfy the constraint
export type OptionsToType<T extends Array<{ name: Array<string>, type: keyof TypeMapping }>>
= { [K in T[number]['name'][0]]: TypeMapping[Extract<T[number], { name: K }>['...
- 97.2k
5
votes
1
answer
5k
views
Extending built-in types in Typescript
I have the following structure:
project
|- types
|- global.d.ts
|- string.d.ts
|- wdio.d.ts
|- src
|- Models
|- Resources
|- Components
|- Extensions
|- string.ts
...
- 594
5
votes
1
answer
9k
views
TS1238: Unable to resolve signature of class decorator when called as an expression
I am seeing the following compilation error:
TS1238: Unable to resolve signature of class decorator when called as
an expression.
Here is the code:
const fdec = function(target:any, field: any, ...
- 97.2k
5
votes
1
answer
6k
views
How to fix Type not assignable to LibraryManagedAttributes for react router render prop
I recently updated all react libraries to the latest and all of its typings. I am facing an issue with typescript compilation. It is saying
[ts] Type '{ history: History<any>; location: ...
- 1,323
5
votes
0
answers
596
views
How can I use multiple wildcards in Typescript module declarations?
In my ReactJS project I use the svg-transform-loader package in WebPack which updates some colors of my SVGs on the fly.
import starOutlineIcon from 'images/star-outline.svg'
import ...
- 286
4
votes
2
answers
537
views
Conditional types with TypeScript
Say I have this:
type TypeMapping = {
Boolean: boolean,
String: string,
Number: number,
ArrayOfString: Array<string>,
ArrayOfBoolean: Array<boolean>
}
export interface ElemType ...
- 97.2k
4
votes
2
answers
902
views
Declare arbitrarily nested array (recursive type definition)
Say I have a function like:
const nested = function(v: string | Array<string> | Array<Array<string>>){...}
the problem is v might be nested 5 or 6 levels deep. How can I declare a ...
user5047085
4
votes
2
answers
4k
views
tsc creates src folder in dist
I have this folder structure:
- src
- subdir1
- subdir2
This is my tsconfig.json:
{
"compilerOptions": {
"target": "es2015",
"module": "commonjs",
"sourceMap": true,
"...
- 12.8k
4
votes
1
answer
6k
views
Argument of type '(event: BlahEvent) => void' is not assignable to parameter of type 'EventListenerOrEventListenerObject'
I've read and tried suggestions found in Argument of type '(e: CustomEvent) => void' is not assignable to parameter of type 'EventListenerOrEventListenerObject' but haven't been ...
- 73.8k
4
votes
0
answers
289
views
How to use interfaces from a .d.ts file outside the current project through project references in TypeScript?
I am new to TypeScript. I am working on a React frontend and Express backend project. My project folder structure is like the following:
server/
├─ src/
│ ├─ index.d.ts
│ ├─ someFile.ts
├─ tsconfig....
- 724
4
votes
0
answers
7k
views
Argument of type 'any' is not assignable to parameter of type 'never'
got this error below,
error TS2345: Argument of type 'any' is not assignable to parameter of type 'never'.
HandEvaluator.prototype.evaluateStraight = function (hand) {
var consecutives = [];
...
- 91
3
votes
2
answers
3k
views
What's the difference between TypeScript const assertions and declarations?
I just read about the new const assertion feature in TypeScript 3.4 RC and I'm not seeing how it does anything differently from using const declarations.
I tested this out using an example from the ...
- 3,916
3
votes
1
answer
2k
views
Recursively exclude readonly properties in Typescript
I'm pretty sure its my lack of experience utilizing complex generics so I'm hoping someone has ideas on how to accomplish this. My use case is for creating "form types" for my React/Formik form values ...
- 155
3
votes
2
answers
10k
views
Properly extend stream.Transform class with TypeScript
I have this code:
import * as stream from 'stream';
export class JSONParser extends stream.Transform {
lastLineData = '';
objectMode = true;
constructor() {
super();
}
...
- 97.2k
3
votes
2
answers
8k
views
TypeScript 3: property is missing in type
I'm working on a ReactJS app with TypeScript. I was using TypeScript 2.8 with no problem, but 2.9 and 3 give me a new error.
import * as React from 'react';
class ExampleComponent extends React....
- 4,611