functiongetValue(){return42;}constresult=getValue();typeResultType=typeofresult;// ResultType 的类型为 number 1. 2. 3. 4. 5. 在上述示例中,我们使用typeof result获取了变量result的类型,并将其赋值给了ResultType类型。在这种情况下,ResultType的类型将为number。 总结 在TypeScript 中,typeof是一种用于...
"dom","dom.iterable","scripthost"], // 指定我们需要用到的库,也可以不配置,直接根据 target 来获取 /* Specify a set of bundled library declaration files that describe the target runtime environment. */"jsx":"preserve",// jsx 的处理方式(保留原有的jsx格式)"module":"commonjs",// ...
getFullName();//应有1个参数,但获得0个getFullName({ age: 18, phone: 110 });//类型“{ age: number; phone: number; }”的参数不能赋给类型“{ firstName: string; lastName: string; }”的参数。getFullName({ firstName: "Hello" });//缺少必要属性lastName 这些都是在编写代码时 TypeScrip...
objectVariable instanceof ClassName ; 来看一个例子: class CreateByClass1 { public age = 18; constructor() {} } class CreateByClass2 { public name = "TypeScript"; constructor() {} } function getRandomItem() { return Math.random() < 0.5 ? new CreateByClass1() : new CreateByClass2()...
function theCityThatAlwaysSleeps() { let getCity; if (true) { let city = "Seattle"; getCity = function() { return city; } } return getCity(); } 因为我们已经在city的环境里获取到了city,所以就算if语句执行结束后我们仍然可以访问它。 回想一下前面setTimeout的例子,我们最后需要使用立即执行的...
在Javascript 中,可以抛出错误并在 catch 中捕获它。通常这将是一个 error 实例,默认设置为 any。将 useUnknownInCatchVariable 编译选项设置为 true 时,它会隐式地将 catch 中的任何变量设置为 unknown 而不是 any。考虑下面的例子: AI检测代码解析
{// use the export keyword in TypeScript to access the class outsideexportclassEmployee {constructor(name:string, email:string) { }}letalex =newEmployee('alex','alex@gmail.com');}// The Admin variable will allow you to access the Employee class out...
letpasscode="Hello TypeScript";classEmployee{private_fullName:string;getfullName():string{returnthis._fullName;}setfullName(newName:string){if(passcode&&passcode=="Hello TypeScript"){this._fullName=newName;}else{console.log("Error: Unauthorized update of employee!");}}}letemployee=newEmployee(...
TypeScript can usually figure out a more specific type for a variable based on checks that you might perform. This process is called narrowing. Copy functionuppercaseStrings(x:string| number) {if(typeofx==="string") {// TypeScript knows 'x' is a 'string' here.returnx.toUpperCase(); ...
type EventNames='click'|'scroll'|'mousemove';functionhandleEvent(ele:Element,event:EventNames){// do something}handleEvent(document.getElementById('hello'),'scroll');// 没问题handleEvent(document.getElementById('world'),'dblclick');// 报错,event 不能为 'dblclick'// index.ts(7,47): error...