Get loop counter/index using for…of syntax in JavaScript

Question

Caution:

question still applies to for…of loops.> Don\'t use for…in to iterate over an Array, use it

Answer 1

For-in-loops iterate over properties of an Object. Don't use them for Arrays, even if they sometimes work.

Object properties then have no index, they are all equal and not required to be run through in a determined order. If you want to count properties, you will have to set up the extra counter (as you did in your first example).

loop over an Array:

var a = [];
for (var i=0; i

loop over an Object:

var o = {};
for (var prop in o) {
    prop // is the property name
    o[prop] // is the property value - the item
}