Generic types in classes and generic types

This article will introduce TypeScript Generic types of classes and related knowledge of generic types in .

Generics in classes

Define class generics , Constructor receives a generic array , Specify the specific type when creating class instances , And pass the specified type array .

class DataManager<T> {
  //  Constructor passes a generic array 
  constructor(private params: T[]) { }
  getItem(index: number): T {
    return this.params[index]
  }
}
//  Pass an array of types represented by generics 
const data = new DataManager<number>([1, 3, 4])
console.log(data.getItem(0))
console.log(data.getItem(1))
console.log(data.getItem(2))

The generic type

Use interface Define a class , And specify the class as the type of class generic （extends）, When creating an instance , You need to pass the attribute value contained in the generic type .

interface Item {
  name:string
}

class DataManager<T extends Item> {
  constructor(private params: T[]) { }
  getItem(index: number): string {
    return this.params[index].name
  }
}
//  The object passed must contain Item Class contains properties 
const data = new DataManager<Item>([
  {
    name:'jake'
  },
  {
    name:'smith'
  }
])
console.log(data.getItem(0))
console.log(data.getItem(1))

Union type generic parameter

Use the union type to specify the data type received by the generic type .

//  Use a union type to specify that a generic type can receive  number  and  string  Type parameter 
class DataManager<T extends number|string> {
  constructor(private params: T[]) { }
  getItem(index: number): T {
    return this.params[index]
  }
}
const data = new DataManager<string>(['jake','smith'])
console.log(data.getItem(0))
console.log(data.getItem(1))

Use a generic annotation as a concrete type