ActiveJS exposes an AsyncSystemBase class that can be used to create customized AsyncSystem like Systems.
One limitation of AsyncSystem is that it doesn't let you change the type of Units used by it.
With AsyncSystemBase you can create your own AsyncSystem like Systems and use any type of Unit you want as queryUnit
, dataUnit
and errorUnit
.
AsyncSystemBase can be utilized in two ways,
Instead of creating an instance of AsyncSystem where the Units are created internally, you can create the Units yourself and pass them to the AsyncSystemBase directly.
const customAsyncSystem = new AsyncSystemBase(new ListUnit<string>(), // queryUnitnew DictUnit<{ a: number, b: string }>(), // dataUnitnew GenericUnit<number>(), // errorUnitnew BoolUnit(), // pendingUnit{clearErrorOnData: false} // config is optional);// extract the Units from the Systemconst {queryUnit, dataUnit, errorUnit, pendingUnit} = customAsyncSystem;// confirm the type of UnitsqueryUnit instanceof ListUnit // truedataUnit instanceof DictUnit // trueerrorUnit instanceof GenericUnit // truependingUnit instanceof BoolUnit // true
If you don't want to create Units every time you want to create a custom AsyncSystem, you can extend the base class and do the same thing that AsyncSystem does, abstract away the Unit creation in the extended class and only accept typings through generics. This will allow you to be more efficient while still staying flexible.
Example: Create a custom AsyncSystem that uses ListUnit as queryUnit
, DictUnit as dataUnit
and GenericUnit as errorUnit
.
// accept the types for queryUnit, dataUnit and erroUnit as genericsexport class CustomAsyncSystem<Query, Data, Error>// extend the base class and pass the Units with types as genericsextends AsyncSystemBase<ListUnit<Query>, DictUnit<Data>, GenericUnit<Error>> {// accept config options optionally to pass them to the base classconstructor(config?: AsyncSystemBaseConfig<Query, Data, Error>) {// create the Units and pass them to the base class along with the configsuper(new ListUnit(),new DictUnit(),new GenericUnit(),new BoolUnit(),config);}}
type QueryType = number; // type for queryUnit's valuetype DataType = string; // type for dataUnit's valuetype ErrorType = {status: number, message: string}; // type for errorUnit's value// initialize a CustomSyncSystem, pass the types as genericsconst customSystem = new CustomAsyncSystem<QueryType, DataType, ErrorType>();// that's it// checking the types of UnitsqueryUnit instanceof ListUnit // truedataUnit instanceof DictUnit // trueerrorUnit instanceof GenericUnit // truependingUnit instanceof BoolUnit // true
When using a custom AsyncSystem, directly or by extending, there are a few things that you should keep in mind, to get the expected results.
AsyncSystem uses GenericUnit because it's very permissive in what it accepts as its value while other Units only allow a specific data type, this difference in behavior might cause a hung state, for example, if we use a DictUnit as the dataUnit
and we try to dispatch an array
value, it will get ignored and any observer expecting a new value wouldn't receive it. Additionally, pendingUnit
wouldn't be updated automatically. (i.e. It'll stay true
until successful data or error dispatch)
To mitigate this problem, when using a non-GenericUnit as a dataUnit
or errorUnit
, ensure that the value being dispatched is valid and will be dispatched. Every Unit has a wouldDispatch
method for exactly this kind of scenario.