js中es6语法去重set方法

<script>
    let s=new Set()
    s.add(10)
    s.add(20)
    console.log(s);
    let arr=[10,20,30,40,50,50,40,20]
    let st=new Set(arr)
    console.log([...st]);
    let string="hello"
    let str=new Set(string)
    console.log([...str].join(""));
    console.log(str.size);
</script>