enum Direction { NORTH = 3, SOUTH, EAST, WEST, }2.字符串枚举在TypeScript 2.4 版本,允许我们使用字符串枚举。在一个字符串枚举里,每个成员都必须用字符串字面量,或另外一个字符串枚举成员进行初始化。enum Direction { NORTH = "NORTH", SOUTH = "SOUTH", EAST = "EAST", WEST = "WEST", }以上...
Using these enum types in real-world cases is quite straightforward because we can simply declare them as types and pass them as arguments to functions. Because number-based enums automatically increment their values, there’s a potential issue when enum members don’t have explicit initial values...
we cannot useselect_dtypesto choose only text columns if “object” data type is used. Select_dtypes(include=”object”) will return any column with object data type. On the other hand, if we use “string” data type for textual data, select_dtypes(include=”string”) will give just wha...
enum Color { Red = 1, Green, Bluelet color: Color = Color.Green;} 2. 接口 (Interface) 接口用于定义对象的结构,包括属性和方法的类型。接口可以用于类型检查和代码提示。 ```typescriptinterface Person { name: string; age: number;} function greet(person: Person): void { console.log("Hello, ...
interface Person { name: string; age: number; } type x = Person["name"]; // x is string 内置工具类型 Required 将类型的属性变成必选,当缺少属性时,就会报错。 代码语言:javascript 代码运行次数:0 运行 AI代码解释 interface Person { name?: string, age?: number, hobby?: string[] } const ...
2.3 String 类型 2.4 Symbol 类型 2.5 Array 类型 2.6 Enum 类型 使用枚举我们可以定义一些带名字的常量。 使用枚举可以清晰地表达意图或创建一组有区别的用例。 TypeScript 支持数字的和基于字符串的枚举。 1.数字枚举 默认情况下,NORTH 的初始值为 0,其余的成员会从 1 开始自动增长。换句话说,Direction.SOUTH ...
text?: string, onError?: ErrorCallback, start?: number, length?: number): Scanner { let pos: number; let end: number; let startPos: number; let tokenPos: number; let token: SyntaxKind; let tokenValue: string; setText(text, start, length); ...
let strLength: number = (<string>someValue).length; 3.2 as 语法 let someValue: any = "this is a string"; let strLength: number = (someValue as string).length; 四、类型守卫 A type guard is some expression that performs a runtime check that guarantees the type in some scope. —— ...
If we were to debug a program, it is easier to read string values rather than numeric values. Consider the same example of a numeric enum, but represented as a string enum: Example: String Enum Copy enum PrintMedia { Newspaper = "NEWSPAPER", Newsletter = "NEWSLETTER", Magazine = "...
TypeScript enum 反向映射 / 双向映射 All In One TypeScript enum 枚举实现原理 JS enum enumDirection{Up,Down,Left,Right}// jsvarDirection; (function(Direction) {Direction[Direction["Up"] =0] ="Up";Direction[Direction["Down"] =1] ="Down";Direction[Direction["Left"] =2] ="Left";Direction...