When I declared the return type of the function below as {}, eslint flagged an error stating not to use {} as a type because it actually means "any non-nullish value".
After understanding the meaning behind this error, I realize that specifying return type {} allows for returning values of various types.
So, if my intention is to only return an empty object, what should be the appropriate return type to use?
function a(): {} {
return {};
// return 1; // This is NOT ALLOWED
}
If you are looking to learn more about the never type, this is the place to be.
The never type serves as the return type for functions that always throw an exception or never complete their execution.
When using the EmptyObject type, it indicates that all properties within the object must be of type never.
Since no other type can be assigned to never, creating an object with this constraint results in an empty object.
UPDATE:
It may not be immediately clear how this concept can be practically applied.
type EmptyObject = {
[K in never] : never
}
function a(): EmptyObject {
return {};
}
Your assumption that the typescript compiler will block numbers or any other primitive type from being assigned to {} is incorrect.
const test1: {} = 'hello'
const test2: {} = 123
const test3: {} = false
const test4: {} = { foo: 'bar' }
const test5: {} = [1, 2, 3]
const test6: {} = null // Error if strictNullChecks is enabled in tsconfig
const test7: {} = undefined // Error if strictNullChecks is enabled in tsconfig
You may also find it interesting to understand the distinction between object and Object: Learn more about typing objects in TypeScript
type GenericObject = { [key: string]: any };
function a(): GenericObject {
return {};
// return 1; // This is not allowed
}
All properties are keyed with strings and have a type of any
There are various utility types available for these kinds of issues, but I personally haven't explored them extensively.
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