projection.md

id	title
projection	Projection

:::info TypeScript Support

A view model projection object has an associated TypeScript type:

• Type Name - ViewModelProjection
• Package - @resolve-js/core

:::

A view model projection is an object of the following structure:

const projection = {
  // The *Init* function creates the view model's initial state object.
  Init: () => initialState,
  // An event handler function is associated with an event type.
  // It receives the view model's state and an incoming event
  // and returns the updated state.
  [EVENT_TYPE]: (state, event) => {
    ...
    return newState
  }
  [EVENT_TYPE2]: (state, event) => ...
  [EVENT_TYPE3]: (state, event) => ...
  ...
}

An event handler implementation receives the following arguments:

Argument Name	Description
state	The view model's state that is an object of arbitrary structure.
event	An event object.
args	Arguments attached to the request.
context	An object that contains functions and data related to the current operation (see the Event Handler Context section.)

An event handler should return a new state object.

Context

A view model event handler context is an object with the following fields:

Field Name	Description
jwt	The JSON Web Token attached to the request.
encrypt	The user-defined encrypt function.
decrypt	The user-defined decrypt function.