Infinite loop when both arguments have cycles

If both arguments have cycles, like if you’re trying to compare doubly-linked lists, dequal goes into an infinite loop.

repro:

const a: any = {}, b: any = {};
a.next = b;
b.previous = a;

const c: any = {}, d: any = {};
c.next = d;
d.previous = c;

dequal(a, c);

[lukeed]

I may add a dequal/circular mode so that users opt into the added checks only when necessary. While my use case is certainly not everyone’s use case, I’ve never run into this IRL because generally I avoid circular references, especially in something like a UI Component’s state, where “is expensive-X the same as expensive-Y” comes up.

Offering it as a module means that it’s an easy import (or import alias) away. There’d be no API changes. Would be the same pattern as dequal vs dequal/lite now.

Also, re: React. @justinfagnani is right here; there definitely should not be a React-specific offering here. A solution for all circulars is a solution for React. But on that note, fast-deep-equal/react might not do what you think @yuri-scarbaci-lenio … it just skips/avoids the problem.

[lukeed]

Don’t quite have the bandwidth to get into everything you brought up right now, but I will later. For now:

would that implies you will also have the permutations?

It would just be dequal, dequal/lite, and dequal/circular. Initially, I almost broke out a dequal/json (supports less than /lite), but IIRC it was only about 80b smaller and not mega-significantly faster than dequal/lite on its own.

I know this might seem unrelated, but it’s to say that I don’t think of these as “permutations” – instead, they’re expanding scopes/feature sets. The scope coverage depends on the size of the umbrella you pick.

Supporting circular references already implies complex objects, which needs to include dequal by default anyway, and so Circulars is an additive, opt-in feature to that.