TS 中的 as 与 is

Question

as 的作用：

1. 类型断言
2. 类型转换

is 的作用：

1. 类型保护的作用

function isPerson(value: any): value is Person {
    return value && typeof value.name === "string" && typeof value.age === "number";
  }
  
  interface Person {
    name: string;
    age: number;
  }
  
  function printPersonInfo(person: Person | string) {
    if (isPerson(person)) {
      console.log(`Name: ${person.name}, Age: ${person.age}`);
    } else {
      console.log(`Invalid person value: ${person}`);
    }
  }
  
  let person = { name: "John", age: 30 };
  printPersonInfo(person); // 输出 Name: John, Age: 30
  printPersonInfo("Invalid Person"); // 输出 Invalid person value: Invalid Person