Hands-On Design Patterns with React Native

readonly

Since our application is not super big yet, as an exercise, let's replace Immutable.js with readonly from TypeScript:

export type TasksReducerState = {    readonly entities: TaskType[],    readonly isLoading: boolean,    readonly hasError: boolean,    readonly errorMsg: string}

This looks like a lot of repetition. We can use Readonly< T > instead:

export type TasksReducerState = Readonly<{    entities: TaskType[],    isLoading: boolean,    hasError: boolean,    errorMsg: string}>

This looks much cleaner. However, it is not entirely immutable. You can still mutate the entities array. To prevent that, we need to use ReadonlyArray<TaskType>:

export type TasksReducerState = Readonly<{    entities: ReadonlyArray<TaskType>,    // ...}>

The remaining work is to replace ...