编辑代码

class Person {
    private _name:string;
    private _age:number;

    constructor(name:string = "", age:number = 20) {
        this._name = name;
        this._age = age;
    }

    set name(name:string) {
        this._name = name;
    }

    get name():string {
        return this._name;
    }

    set age(age:number) {
        this._age = age;
    }

    get age():number {
        return this._age;
    }
}

let person: Person = new Person();
person.name = "zhangSan";
person.age = 20;

let str:string = JSON.stringify(person);

console.log(str);

let set:Set<number> = new Set<number>();

set.add(1);
set.add(2);
set.add(3);
set.add(3);

console.log(set);

set.forEach(item => {
    console.log(item);
})

let n:any = undefined;
if (n == null) {
    n = "123";
}
console.log(n);