length; TypeScript Union Types and Type Aliases Union Types 代码语言:javascript 代码运行次数:0 运行 AI代码解释 let greet = (message: string | string[]) => { if(message instanceof Array) { let messages = ""; message.forEach((msg) => { messages += ` ${msg}`; }); console.log("...
type Name=string;typeNameResolver=()=>string;type NameOrResolver=Name|NameResolver;functiongetName(n:NameOrResolver):Name{if(typeofn==='string'){returnn}else{reutrnn()}} 类型Name其实就是string的别名,类型() => string,一个函数返回一个字符串,这种格式就是类型NameResolver,NameOrResolver是一个...
示例代码如下：interface IPerson {name: string;age: number;}type allKey1 = keyof IPerson; // 'name' | 'age'type allKey2 = keyof IPerson[]; // 'length | 'toString | 'pop' | 'push' | 'concat' | 'join' | ...type allKey3 = keyof { [x: string]: IPerson }; // string | n...
function createUserId(name: string, id: number): string { return name + id; } 7.4 函数类型 let IdGenerator: (chars: string, nums: number) => string; function createUserId(name: string, id: number): string { return name + id; } IdGenerator = createUserId; 7.5 可选参数及默认参数 ...
function createUserId(name: string, id: number, age?: number): string { return name + id; } // 默认参数 function createUserId( name: string = "Semlinker", id: number, age?: number ): string { return name + id; } 在声明函数时,可以通过?号来定义可选参数,比如age?: number这种形式...
function f(x: unknown) { switch (true) { case typeof x === "string": // 'x' is a 'string' here console.log(x.toUpperCase()); // falls through... case Array.isArray(x): // 'x' is a 'string | any[]' here. console.log(x.length); // falls through... default: // ...
TypeScript has always used a set of rules and guesses for when to reuse type aliases when printing out types. For example, take the following code snippet. Copy export type BasicPrimitive = number | string | boolean; export function doStuff(value: BasicPrimitive) { let x = value; return ...
classT{publicname:string=''publicgreet():void{console.log('Hello, '+this.name); } }classU{publicname:string=''publicgreet():void{console.log('Greetings, '+this.name); } } 能把类型为T的值赋给类型为U的变量吗? letu: U =newT();// 是否允许?
泛型泛型主要是为了解决类型复用的问题。可以说泛型给了你在使用 ts 类型检测的体验同时,又提供了很好的类型扩展性、可维护性。在使用泛型类型时,可以将泛...
(category); }); this.categories.length > 0 && (this.current = this.categories[0]); } }; //IndexedDB初始化及升级 request.onupgradeneeded = (event) => { // Grab a reference to the opened database const db = (event.target as any).result; // Create an objectStore to store our ...