Comments on: Advanced Javascript: Objects, Arrays, and Array-Like objects

By: nFriedly

nFriedly — Wed, 22 Jul 2009 19:50:42 +0000

Hey Dmitriy!

Yea, those are good points, both about arrays not getting their own type and forEach loops hitting inherited items as well as local items. It’s handy when you want those inherited items to be in the loop though.

Similarly, live collections can be really handy, as long as you realize they’re live

By: illvm

illvm — Tue, 14 Jul 2009 05:01:26 +0000

There is no array type in JS though. All arrays are objects! typeof [] === ‘object’; Even more confusing is HTMLCollections appear to be arrays when they are, indeed not, and inherit from a separate prototype. On top of that they are live collections and need to be cloned or otherwise cached if you are modifying them in some way (especially adding to or removing from).

What’s really unfortunate is that for in loops are deceptively not forEach loops. They iterate over every key in the object on the right side of the in without regard to whether that key is actually part of that object! I don’t really see an issue with the for in loops using ‘two’ as an index though, it seems proper. For in returning prototype keys instead of objects keys though can be a real mess. =/

By: nFriedly

nFriedly — Thu, 18 Jun 2009 14:40:38 +0000

Yes, I think an Objects and Arrays both fall under the description of collections.

In PHP, array() can be an associative array (like an Object in javascript) or a numerical array (like an Array in javascript), there’s only one object.

PHP also has Objects, which are roughly comparable to javascript objects. So really in PHP, there’s two ways to do it.

When a PHP array() is used as an associative array, the items are in a guaranteed order. In a javascript Object, the items are usually in whatever order you added them, but it is not guaranteed.

By: Mahbub

Mahbub — Thu, 18 Jun 2009 10:03:27 +0000

We call Javascript object arrays as collection, isn’t it? In php the similar is called an associative array.

By: Hardik Thakkar

Hardik Thakkar — Fri, 12 Jun 2009 07:14:45 +0000

Really appreciate your article ideas and techniques to make javascripts much faster.

Today i really got to know something new about javascript technology.

Thanks for giving essential information about javascripts.

By: SMercer

SMercer — Thu, 11 Jun 2009 15:07:00 +0000

Great article. It’s easy to forget the foundations of javascript when you get so comfy with frameworks.