Flow type, What does the `+` symbol mean in front a property?

Question

I came across the following code written in js FlowType (I am interested to know the value of + in the context of FlowType not in general JS).

Could you please expla

Answer 1

After some additional research I found out that +/- indicate the covariant or contravariant for a property.

interface MyInterface {
  +covariant: number;     // read-only
  -contravariant: number; // write-only
}

Interesting article on variance:

https://flow.org/en/docs/lang/variance/

https://flow.org/en/docs/types/interfaces/#toc-interface-property-variance-read-only-and-write-only

Answer 2

The + symbol in front of the property means the property is read-only

Reference: https://flow.org/en/docs/types/interfaces/#toc-interface-property-variance-read-only-and-write-only

Answer 3

The '+' symbol means the property is read only and
'-' means the property is write only and
If does not have any '+' or '-' symbol it means the property have both read/write access.
It can be used while defining interface property or type property.

The documentation can be found in below link:
https://flow.org/en/docs/types/interfaces/#toc-interface-property-variance-read-only-and-write-only