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Equality of Data Structures: Ruby vs. JavaScript

Anna Rankin on April 07, 2019

Skip to the TL;DR In recent weeks I've been reading through JavaScript Allongé by Reginald Braithwaite (an excellent look at the fundamentals of J...

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Nick Taylor • Apr 7 '19

Same box vs same stuff in the boxes. Great analogy.

Anna Rankin • Apr 7 '19

Thank you Nick! 😁

AhmadDeel • Apr 8 '19 • Edited

Great post but two notes:
First => on my personal experience js checks if two objects are the same; I mean if they have the same reference. Like:
Const b = {
value:1
};
Const a = b;
a === b // true

I didn't test that for arrays. And you mentioned that js checks to see if the two thing are equal (in value ? ) sounds to me like js is checking their references. Am I right ?

Second => I think the place of TL;DR should be at the top of this post.
Happy coding.

Anna Rankin • Apr 9 '19

Hi Ahmad - this is correct! For data structures, it does check to see if the two things being compared point to the same reference in memory - for primitives, it compares the items by value. I'd originally had a bit in the article about reference vs identity, but I chopped it out because it was getting convoluted 😳And I think you're right, the TL;DR would be better suited at the beginning. Thanks for your input 🙌

Tim Supinie • Apr 9 '19

I guess isn't Javascript's == operator supposed to be an "is this the same stuff in the box" check? There's all this implicit typecasting going on, but at its heart, it's an equality check designed to determine if two variables contain the same value. So I'm not sure you can draw the conclusion of philosophical differences in language design when Javascript has an operator with the same intent as in Ruby.

Anna Rankin • Apr 9 '19

Hi Tim, good point! However, if you try out [1,2,3] == [1,2,3] in your console, you'll see it returns false. JS's double-equals will coerce types, but it won't perform a recursive equality check the way it does in Ruby. 😵