This is a typing construct in Typescript (2.1+) which allows static typing for dynamically named properties. Basically, the new type will be a union of all available key properties in an object.
Questions tagged [keyof]
141 questions
1
vote
2 answers
typescript 'keyof' change the origin property optional?
Define an interface like this
interface Props {
a?: string
b?: string
c?: string
d: string
}
When I do something like this, it is ok
type Test1 = {
[P in keyof Props]: Props[P]
}
const a1: Test1 = {
d: '1'
}
but, like this, I got some…
Ben
- 73
- 1
- 5
1
vote
2 answers
Recursive type definition with mapped and conditional types
I'm trying to come up with a way to have better type safety with TypeORM. The following are some example TypeORM entity definitions.
import { BaseEntity, Entity, Column, ManyToMany, JoinTable, ManyToOne, OneToMany } from 'typeorm';
@Entity()
class…
Utku
- 2,025
- 22
- 42
1
vote
1 answer
Typing for key by generic type lookup
I'm trying to get strong typings like this:
enum Schema {
content = 'content',
interaction = 'interaction',
}
type ContentData = {
content: string;
};
type Data = Record & {
[Schema.content]: ContentData;
}
type Event
Sergej
- 1,082
- 11
- 27
1
vote
0 answers
Make typescript parameter keyof K and typeof FormGroup
I want to pass in an object which is key of a class K and has the type of or extends FormGroup like:
public async myMethod(
...
formGroupName: keyof K & typeof FormGroup) { }
So wenn I call it then, the keyof K seems to work as I…
jo-chris
- 362
- 6
- 13
1
vote
0 answers
typescript loop object rewrite self property
function resetForm () {
// const INITIALFORM = {
// url: '',
// device: 'mobile',
// dimension: ['time', 'page'],
// }
for (const key in INITIALFORM) {
type KeyType = keyof typeof INITIALFORM
const…
mihuar
- 13
- 3
1
vote
1 answer
TypeScript: keyof unexpected behavior
class Target {
prop1 = "321";
}
const target = new Target()
class Target2 {
prop2 = "123";
}
const target2 = new Target2()
type TValue = {
target: V;
key: keyof V;
}
class Case[]> {
…
Just Alex
- 183
- 1
- 12
1
vote
2 answers
Typesript argument depends on another argument with a default value
I am trying to make a function in typescript where the second, optional argument, is a key of the first argument. Without the optional argument, the function I want looks like
function getVal(obj: T, key: keyof T) {
return…
Jason Siefken
- 737
- 7
- 12
1
vote
1 answer
How to dynamically assign values to object properties in Typescript?
I have these two types:
type ArbitraryPropertyName = keyof typeof arbitrary;
type D = { [k in ArbitraryPropertyName]: any };
Now I want to declare a variable of type D, but I don't want to assign each arbitraryPropertyName one by one, like…
but-why
- 533
- 3
- 10
1
vote
0 answers
TypeScript: get the type of the value of generic object property with keyof T
I have looked at similar questions here here here and here that so far have not helped resolve my issue. Apologies if there is overlap that I was not able to extract.
I'm having a really tough time explaining my issue, so here goes my best…
BradStell
- 371
- 3
- 17
1
vote
1 answer
In TypeScript, how can I infer my arguments and impose a constraint that all items be keyof T, where T is the generic type for the function?
My goal here is to create a function named: getFields. This function has a generic and a parameter ...fields: Array. I would like this function to return a function which when given an object of type will return a reduced object…
Will McCullough
- 31
- 2
1
vote
2 answers
is there a way to describe a kind of "keyfor" in typescript?
is there any way to express that a key-property for an object should be limited by related value? Something equivalent to keyof but for the value related to given key?
const objectAction = (obj: T): void => obj;
const…
m. maylon
- 13
- 2
1
vote
2 answers
Typescript function where object has a property of type string determined by another parameter
I want to create a TypeScript function that takes an object and a property within that object, for which the value is a string. Using works to make sure only keys of T are allowed as values for the property, but I cannot seem…
JHH
- 8,567
- 8
- 47
- 91
1
vote
1 answer
How to represent group of data as a generic Typescript interface
In short:
How can I declare, using Typescript type's system, a generic interface which takes as type parameters
a type Gof a group (all the properties that belong to a group)
a type I of an item in the group (all the properties of an item, of which…
MaxAxeHax
- 423
- 7
- 14
1
vote
1 answer
Why does this TS implementation of "prop" work but mine does not?
I was looking through some blogs about how to use the keyof feature of typescript to implement a classic function in Ramda/Underscore called prop which returns the value corresponding to a given key on a certain…
Luís Hendrix
- 156
- 2
- 6
1
vote
3 answers
typescript: enforcing existing object keys
I would like dropdownAttributes to limited to attributes on DropDownItem interface.
interface DropDownItem {
[key: string]: any;
}
interface Props {
dropdownList: DropDownItem[];
dropdownAttributes: string[];
}
if DropDownItem did now…
pethel
- 5,397
- 12
- 55
- 86