Example of compact JSDoc type definitions.

.js

/** Definition for item.
  @typedef {{
      key: number,
      value: string
    }} Item
 */

/** The property `items` is an array of type Item.
  @typedef {{
    newKey: number,
    inputValue: string,
    items: Item[]
  }} State
 */

/** This type's methods return Message objects that are sent to the program's update method and processed by the action methods.
  @typedef {{
    updateInputValue:(value: string) => State,
    addItem: () => State,
    deleteItem: (key: number) => State,
    useFetchedData: (data: State) => State
  }} ActionMethods
 */

/** This is the type for the object of methods used in Msg.match of the update function to trigger the correct actions for the received message.
  @typedef {{
    match: (msg: Message, Object: ActionMethods) => State,
    updateInputValue: (value: string) => State,
    addItem: () => State,
    deleteItem: (key: number) => State,
    useFetchedData: (data: State) => State
  }} MessageUnion
 */