Deep vs. shallow copy

[PastCoder]

Hi Miguel,
after 7 years your implementation is still a helpful and easy to understand implementation.
Thanks for providing it!

Just one thing took me a while of debugging (i.e. because in Javascript I am more a trial-and-error developer):
In der function breed() the slide does only a shallow copy of the best half of the population. As I am using more complex structures as individuals, this caused the problem that the individuals did still have some shared references so that I lost my best indivduals when modifying others.

After I did the following change, it worked:
Instead of
let newPopulation = population.slice(0, breeders);
I use now
let newPopulation = JSON.parse(JSON.stringify(population.slice(0, breeders)));

Maybe this solution would make your implementation more robust also for complex structures.

Edit:
It seems there are a few more places like
let parentA = JSON.parse(JSON.stringify(population[parentAIndex].individual));
let parentB = JSON.parse(JSON.stringify(population[parentBIndex].individual));

[lodenrogue]

Nice solution. I'll have to test it a bit and see how it performs in some other test cases.