如何...循环语句在Javascript中工作？（ECMAScript 6）

Question

I have a snippet which I'm experimenting the for...of statement on it:

let arr = [3, 5, 7];
arr.foo = "hello";

for (let i in arr) {
   console.log(i); // logs "0", "1", "2", "foo"
}

for (let i of arr) {
   console.log(i); // logs "3", "5", "7"
}

My Question is that for...of should run on iterable values, right? so why the second for doesn't print "hello" ?

Answer 1

Arrays are iterables over their elements . That's how it's defined. That is how Array[Symbol.iterator] is implemented.

See http://www.2ality.com/2015/02/es6-iteration.html .