_ 误导，js 不存在 private

TypeScript Types

Any, Void, Never

Interface, Tuple, Enum

# TypeScript Types

https://www.typescriptlang.org/docs/handbook/basic-types.html

https://www.typescriptlang.org/docs/handbook/advanced-types.html

```ts

Boolean

Number

String

Array

Tuple

Enum

Any

Void

Null and Undefined

Never

Object

// Type assertions

// A note about ‘let’

```

```ts

Intersection Types

Union Types

Type Guards and Differentiating Types

  User-Defined Type Guards

    Using type predicates

    Using the in operator

  typeof type guards

  instanceof type guards

Nullable types

  Optional parameters and properties

  Type guards and type assertions

Type Aliases

  Interfaces vs. Type Aliases

String Literal Types

Numeric Literal Types

Enum Member Types

Discriminated Unions

Exhaustiveness checking

  Polymorphic this types

Index types

  Index types and index signatures

Mapped types

  Inference from mapped types

Conditional Types

  Distributive conditional types

  Type inference in conditional types

  Predefined conditional types

```

https://www.typescriptlang.org/docs/handbook/utility-types.html

```ts

Partial<T>

Readonly<T>

Record<K,T>

Pick<T,K>

Omit<T,K>

Exclude<T,U>

Extract<T,U>

NonNullable<T>

Parameters<T>

ConstructorParameters<T>

ReturnType<T>

InstanceType<T>

Required<T>

ThisParameterType

OmitThisParameter

ThisType<T>

```

TS 常见类型

Boolean Number String Array

Tuple Enum interface class

Any Void Null Undefined Never(某个函数不可返回)

变量声明

const/var/let 变量: 类型

函数声明

function 函数名(参数1: 类型1, 参数2: 类型2): 返回类型 {}

箭头函数

(参数1: 类型1, 参数2: 类型2):返回类型 => {}

类成员的声明

class 类名 {

    // 私有变量

    private _x: number;

    private _y: number;

    ...

}

未声明类型默认作为 any 类型

声明类成员类型、方法/函数的参数类型和返回类型

能明确推导时 局部变量/箭头函数 可以不申明类型

ts小结：

申明类型-函数

申明类型-变量/常量

const 常量名：类型

let 变量名：类型

var 变量名：类型

TypeScript的常见类型

TypeScript在JavaScript里面独有的语法

typescript的常见类型