Sort attributes by the type of property

Question

Sort attributes by the type of property

Is there a way to create a customized type by extracting specific properties from a generic type?

class Test {
  value1!: Date
  value2!: number
  value3!: Date
  value4!: string
}
type FilterProperties<T, TFieldType> = //looking for a solution to select fields of the type TFieldType only
const onlyDates = {} as FilterProperties<Test, Date>

FilterProperties<Test, Date>

should ideally contain only the properties value1 and value3.

I attempted using Extract and Pick, but they operate based on keys rather than types.

typescript generics

Answer 1

Answer №1

Here is a useful technique you can apply:

class Example {
  item1!: Date
  item2!: number
  item3!: Date
  item4!: string
}

type SelectItems<T, TFieldType> = {
    [K in keyof T as T[K] extends TFieldType ? K : never]: T[K]
}

type C = SelectItems<Example, Date>
/*
type C = {
    item1: Date;
    item3: Date;
}
*/

Answer 2

Here is a useful technique you can apply:

class Example {
  item1!: Date
  item2!: number
  item3!: Date
  item4!: string
}

type SelectItems<T, TFieldType> = {
    [K in keyof T as T[K] extends TFieldType ? K : never]: T[K]
}

type C = SelectItems<Example, Date>
/*
type C = {
    item1: Date;
    item3: Date;
}
*/

Sort attributes by the type of property

Answer №1

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