Opt-out of truncation for custom classes?

The https://github.com/astorije/chai-immutable plugin extends lots of core assertions to work with ImmutableJS.

The collections in Immutable all have a custom toString() and inspect() method which produces a readable version of their internal datastructures. This gets picked up correctly by chai’s inspect util.

However, if this representation goes over the truncateThreshold, they are detected as objects and their first two properties are displayed instead - which isn’t useful for these collections.

To work around this, many of the assertion methods convert the objects to a string before passing to the message formatting. This mostly works but it’s easy to miss cases.

This problem should apply to any object with a custom inspect, would it be possible to tweak this behaviour somehow?

Some options I can think of would be to change the object detection to check for plain objects only, or to skip truncation for objects with a custom inspect() method, or to truncate the result of inspect() when objects have an inspect().

Any thoughts?

Two options I can think of

[glenjamin]

In the best case scenario, it uses Chai’s custom inspect utility, which is a close adaptation of Node’s util.inspect, although work is being done here to improve upon that. This plays nicely with Immutable collections thanks to their custom .toString property. It’s important to note that at no point in this process does Chai take into consideration an object’s .inspect property.

Immutable objects have .inspect() as an alias for .toString(), as far as I can tell this is what chai and/or loupe would pick: https://github.com/chaijs/chai/blob/master/lib/chai/utils/inspect.js#L45 https://github.com/chaijs/loupe/blob/master/lib/loupe.js#L61

On a related note, you may find https://github.com/Xotic750/inspect-x interesting, it’s also originally based on Node’s inspect and does a good job of handling the newer ES6 datatypes.

Personally, I’m not too crazy about how it’s handling arrays and objects. I think I’d prefer that it instead take the original .toString representation and cut it down to truncateThreshold length by chopping off from the end. And then adding a “…” at the end of it. I believe this would be more helpful in general, not just in your examples with the Immutable library, and would still respect the user’s truncateThreshold setting.

👍 from me on this, assuming you mean the result of the inspect util (and loupe in future). that would solve my immediate problem and should work well in general. Would you still want to handle values that were originally strings differently?

I’m also not in favor of Chai having knowledge of an object’s .inspect property. Unlike .toString, there’s nothing standard about .inspect.

I think it’s reasonably fair to say it’s a de-facto standard in Node-land, thanks to https://nodejs.org/dist/latest-v4.x/docs/api/util.html#util_custom_inspect_function_on_objects having been in the docs since at least 0.4 that I know of. Whether that’s a good enough reason to lean more heavily on it, I don’t know.

[glenjamin]

That seems sensible, please let me know if there’s anything on there that I could help contribute with.