// 用法一：物件轉陣列
        // example 1:
        let obj = {0:'a',1:'b',2:'c',length:3}
       console.log( Array.from(obj) );// [a,b,c]

// example 2: 這個寫法和展開操作符是一樣的，為了簡便，還是用展開操作符吧
        let div = document.querySelectorAll('div')
        console.log(Array.from(div));
        let divCopy 
 
= [...div]
        console.log(divCopy);

        // 用法二：set轉陣列,使用展開操作符也是一樣
        let set  = new Set([1,2,3])
        console.log(Array.from(set));
        let a = [1,2,3]
        let set2 = new Set(...[a])
        console.log([...set2]);

        // 用法三：Array.from的第二個引數，可以遍歷陣列,相當於map和forEach
        let b = [1,2,3]
        console.log(Array.from(b,v
 
=>v+2)); // [3,4,5]
        Array.from(b).forEach(v=>console.log(v+2))
        Array.from(b).map(v=>console.log(v+2))

Array.from和Array.of對比

Array.of是把一組值轉換為陣列

 Array.of(1,2,3) // [1,2,3]