Using new Array(n) constructor in snapshot doesn't work

[davetapley]

Bug report

• I've checked documentation and searched for existing issues
• I've made sure my project is based on the latest MST version
• Fork this code sandbox or another minimal reproduction.

Sandbox link or minimal reproduction code
https://codesandbox.io/s/mobx-state-tree-using-new-array-n-constructor-in-snapshot-doesnt-work-ehd5ib

Describe the expected behavior
If I use Array.new(3) for a types.array(types.maybe(types.number)) it should be [undefined,undefined,undefined].

Describe the observed behavior
It is put in the store as an empty array [].

Even crazier
If you a = Array.new(3); a.fill(undefined), then it correctly inserts [undefined,undefined,undefined] 🤯

[diegochavez]

Hi Dave,

New Array generates an array with a length of 3, not including values. that's way is undefined
the generated array looks like this.
[key]:value
0:undefined
1:undefined
2:undefined

For new array from a number you should do,
const stuff = [...new Array(3).keys()];
const stuff = Array.from(new Array(3).keys());

[coolsoftwaretyler]

Hey @davetapley - did the response from @diegochavez solve your problem? If so, let me know and we can close this out.

Since it's been over a year since there was activity here, I'll probably close this out if I don't hear from any of y'all in the next two weeks or so.