疑问：TS

https://www.typescriptlang.org/docs/handbook/typescript-in-5-minutes.html

TypeScript in 5 minutes

Compiling your code（编译代码）

tsc greeter.ts // 返回 greeter.js 文件

• Add a : string type annotation to the ‘person’ function argument as shown here（为 person 添加类型注释）

function greeter(person: string) {
    return "Hello, " + person;
}

let user = "Jane User";

document.body.textContent = greeter(user);