What are interface and type?

Interface is the type of an interface

• Can be extended (“Extends and implements”)
• Properties merging (“Declaration merging”)

Type is a type alias

• Basic types can be aliased

Both type and interface work

When they describe an Object, they are very similar

// interface
interface IPerson {
    firstName: string
    lastName: string
}
interface Iadd  {
    (x:number.y:number) :number
}
  
// type
type Person = {
    firstName: string
    lastName: string
}
type Add = {
    (x:number.y:number) :number
};
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Type works and interface doesn’t

Primitive type aliases, union types, tuples, and so on

// Base type alias
type id = number

// Union type
type Names = "zhangsan" | "lisi";

// Specify the type of each position in the array
type List = ["abc".number]

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Use Typeof to get the instance type for assignment

// Typeof performs the assignment
const initialState = {
  todos: [] as Todo[],
};
type TodoState = typeof initialState;
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Interface works and type doesn’t

A statement to merge

// declare the merged IPerson to contain firstName, lastName, nickName attributes
interface IPerson {
  firstName: string
  lastName: string
}

interface IPerson {
  nickName: string
}

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How to use better?

use whatever suites you and your team, just be consistent

Interface and type can be used, but it is important to keep the whole team consistent