in JS, what is the itemKey parameter for index(itemKey)? and how am i suppose to know it?

[mecdos]

almost every collection in illustrator seems to have the method index(itemKey) that gets an element from the collection with itemKey being 'string, number'

but what is that string and number? how do i find what the "itemKey" of an object is? it's not something i can assign, so when does one use this method without knowing what the itemKey is?

[femkeblanco · Accepted solution]

https://community.adobe.com/t5/illustrator/could-someone-please-explain-how-to-use-the-index-method/... 

[Inventsable]

Where's this information coming from? When I iterate through the keys of collections like PathItems or PageItems, there's no index key or method.

[femkeblanco]

It's in the JS Scripting Reference (including the most recent one). 

[Inventsable]

Odd, I get undefined trying to explicitly call it. Not sure why there'd be a method for it in the first place instead of using bracket notation though.