In the following code ( Try Flow ):
type Response = {
err: ?string;
data: Object;
}
function length(x): Response {
return { data : {} };
}
length(10)
I made err
optional, but still get an error:
Property
err
not found in object literal
This is the correct syntax for an optional property:
type Response = {
err?: string;
data: Object;
}
The syntax you tried to use ( err: ?string
) is a Maybe type , which means the err
key should be in the object and can have type string
, null
, or void
( undefined
).
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