Cross-platform Desktop Application Development: Electron, Node, NW.js, and React

Enum type

Time after time, we use constants to define a set of logically related entities. With TypeScript, we can declare an enumerated type populated with immutable data and then refer to the whole set by the type:

const enum Status { 
    NEEDS_PATCH, 
    UP_TO_DATE, 
    NOT_INSTALLED 
} 
 
function setStatus( status: Status ) { 
  // ... 
} 
 
setStatus( Status.NEEDS_PATCH ); 

Here, we declare a type Status that accepts one of the predefined values (NEEDS_PATCH, UP_TO_DATE, and NOT_INSTALLED). The function setStatus expects the status parameter to be of the Status type. If you pass in any other value, TypeScript reports an error:

setStatus( "READY" ); 
//  error TS2345: Argument of type '"READY"' is not assignable to parameter of type 'STATUS'. 

Alternatively, ...