Type of `data` not corresponding to the initialData

[viclafouch]

Describe the bug
The type of data is not corresponding to the initialData. How to avoid this undefined type ?

I thought this PR (#2069) fixed the issue :/ (I already remove my node_modules and npm i).

it starts off with printing data is[], type is not undefined, and then after 2 seconds, I have my array filled, type is still not undefined.

Desktop (please complete the following information):

• OS: Chrome
• Browser: 89.0.4389.128
• Version: 3.13.10

[TkDodo]

data is always potentially undefined on type level. initialData cannot narrow the type.

see also: #1301