for ... of

无法取到index，只能取到value。 原生的Object不可以使用for of

for of与for in的区别

Both for...in and for...of statements iterate over something. The main difference between them is in what they iterate over.

The for...in statement iterates over the enumerable properties of an object, in an arbitrary order.

The for...of statement iterates over data that iterable object defines to be iterated over.

可使用for in的类型

• Array
• String
• arguments (an array like object)
• NodeList
• TypedArray (new in ES2017)
• Map
• Set