Every other object must use the `immerable` symbol to mark itself as compatible with Immer. When one of these objects is mutated within a producer, its prototype is preserved between copies.
```js
import{immerable}from"immer"
classFoo{
[immerable]=true// Option 1
constructor(){
this[immerable]=true// Option 2
}
}
Foo[immerable]=true// Option 3
```
For arrays, only numeric properties and the `length` property can be mutated. Custom properties are not preserved on arrays.
When working with `Date` objects, you should always create a new `Date` instance instead of mutating an existing `Date` object.
Maps and Sets that are produced by Immer will be made artificially immutable. This means that they will throw an exception when trying mutative methods like `set`, `clear` etc. outside a producer.
