Object.assign Side Effects and How To Copy

In How To Copy Objects post I'll explain the difference between various native ways to copy own keys and properties, describing also the fact that Object.assign is full of surprises and side effects.

As example, assigning to an object something like {get next() {return ++this.i}, i:0} instead of {i:0, get next() {return ++this.i}} will result in different values copied over: next === 1 and i === 1 in the first case, next === 1 and i === 0 in the second one.