Typescript - 返回作为整个接口一部分的类型（检查它是否实现了其他接口）

Question

I have a generic reducer that's return type is TableState.

const reducerFactory = ..... = (): TableState => ....

TableState:

 interface TableState {
  filters: Filter;
  data: TableData;
  isLoading: boolean;
}

Each component's that uses this reducer factory implements TableState. For example

interface SalesReportState implements TableState {
  someCommonField: string;
}

App build fails as the types don't match. I could do someCommonField?: string; but someCommonField should be obligatory.

Is there a Typescript feature that the return type just checks if the table type implements Table State? So the return type would be some type that makes sure it is an instance of TableState, not exactly TableState type.

Answer 1

If you want to know if an object implements TableState , you can use:

1. instanceof
\n

 
 
  
  if (obj instanceof TableState) // returns true if object implements TableState
 
 

only works with abstract class

2. type-guards . Example:

let obj = {}; // an object you want to check

/**
  * A discriminator is a property which determines if the object in question is
  * a TableState 
  */

function isTableState(obj: any): obj is TableState {
  return obj &&
    obj.filter &&
    obj.data &&
    obj.isLoading && typeof(obj.isLoading) === 'boolean';
}

// check phase
if (isTableState(obj)) {
  // object is automatically casted to TableState
}

PS: If you want to extend an interface with another interface, use extends EDIT: I don't know the Filter and TableData type, is that an interface or a class? The answer may change again, depending on the type