function f(x = 10) { // ... } 现在在 f 函数体内,x 的类型为 number,因为任何 undefined 参数都会被替换为 10。注意当一个参数是可选的,调用的时候还是可以传入 undefined:declare function f(x?: number): void; // cut // All OK f(); f(10); f(undefined); ...
function loggingIdentity<Type>(arg: Type[]): Type[] { console.log(arg.length); return arg; } 你可以将 loggingIdentity 的类型读取为 “通用函数 loggingIdentity 采用类型参数 Type 和参数 arg(Type 的数组),并返回 Type 的数组。” 如果我们传入一个数字数组,我们将返回一个数字数组,因为 Type 将绑...
function filter1<Type>(arr: Type[], func: (arg: Type) => boolean): Type[] { return arr.filter(func); } function filter2<Type, Func extends (arg: Type) => boolean>( arr: Type[], func: Func ): Type[] { return arr.filter(func); } 1. 2. 3. 4. 5. 6. 7. 8. 9. 我...
functionf(x =10) {// ...} 现在在f函数体内,x的类型为number,因为任何undefined参数都会被替换为10。注意当一个参数是可选的,调用的时候还是可以传入undefined: declarefunctionf(x?:number):void;// cut// All OKf();f(10);f(undefined); 回调中的可选参数(Optional Parameters in Callbacks) 在你学习...
declarefunctionintersect<T, U>(x: T, y: U): T & U; function foo<T extends"abc"|"def">(x: T, str:string,num: number) { // Was 'T &string', nowisjust 'T'leta =intersect(x, str); // Was 'T & number', nowisjust 'never'letb =intersect...
declare module Module_Name { } TypeScript 引入声明文件语法格式:/// <reference path = " runoob.d.ts" />泛型 function makeState<S>() { let state: S function getState() { return state } function setState(x: S) { state = x } return { getState, setState } } // 限制它就只能输入...
declarefunctionfn<Valueextends1|2>(...args:Valueextends1?Parameters<(x:number)=>void>:Parameters<(y:number,name:string)=>void>):void;fn<1>(42);fn<1>(42,"hello world");// Error: expects 1 argumentfn<2>(42);// Error: expects 2 argumentsfn<2>(42,"hello world"); ...
declarefunctionrequire(moduleNames: string[], onLoad: (...args: any[]) =>void):void; import* as Zip from "./ZipCodeValidator";if(needZipValidation) { require(["./ZipCodeValidator"], (ZipCodeValidator:typeofZip) =>{ let validator=newZipCodeValidator.ZipCodeValidator();if(validator.isAcceptabl...
declare enum Enum { A = 1, B, C = 2, }复制代码 1. 2. 3. 4. 5. 泛型 为了提高代码复用率,泛型可以允许指定类型参数,来创建逻辑相同的代码片段(类型,类,函数),例: function identity<T>(arg: T): T { return arg; }let output = identity<string>("myString");复制代码 ...
What is declare? What is the difference between unknown, void, null and undefined, never in ts? What are generic constraints in ts? Two ways to define an array type Type assertion in ts Generic functions and generic interfaces How to understand as const?