How for...of Loop Statement Works in Javascript?(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"?

Bergi · Accepted Answer · 2015-06-27 18:02:46Z

5

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.

edited Jun 27, 2015 at 18:02

Bergi

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answered Jun 27, 2015 at 17:13

user663031

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2 Comments

Ramin Omrani Over a year ago

so you mean foo is a property, not an element. but aren't array indexes, properties themselves?

user663031 Over a year ago

0 and foo are both properties, while 3 is an element but hello is not. Elements are the values that occur as values of integer-valued properties.

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