Warning: "mutating the [[Prototype]] of an object will cause your code to run very slowly;"

[Marie]

I don't know enough about javascript objects/prototypes to know if this is a real issue and I dont know if you already knew about this but just in case...

mutating the [[Prototype]] of an object will cause your code to run very slowly; instead create the object with the correct initial [[Prototype]] value using Object.create

I just noticed this warning in the console of Firefox 39.0. The error points to line #483, in fixPrototype.

Just from reading a few questions/issues on Stackoverflow/Github it seems like the issue is with the fact that newer Javascript engines optimize objects on creation and manually overriding proto undoes that.

[Christopher Wellons]

The problem is that the object is created by JSON.parse with no
opportunity to use Object.create. Take a look at the "else" clause just
below the linked potion, where it makes a copy using Object.create. This
is a fallback for browsers without support for proto (Internet
Explorer < 11), though now that proto has been standardized in ES6
this need should be diminishing.

There's a trade-off at play here, but I don't have any benchmarks to
know the actual costs involved. The way it's written now, deserializing
is faster because a copy isn't made, but resurrected methods will have
extra overhead due to proto meddling. I could drop the use of
proto and always create a copy. This would slow down serialization,
but the copy would have better method performance.

I guess ultimately this should be a configuration option, just like
"cleanup" is an option. But I don't know if I want to bother with it
until I see some performance benchmarks that show it could matter.