datem

Datem provides abstract datum types. Datum types represent a value and an additional flag indicating if the value has been set. They present constant objects whose actual values may be changing.

Datum objects are event emitters - listeners can be notified whenever the value changes or an error is handled.

Datum Types

• SET_EVENT ( datum, value )
• CHANGE_EVENT ( datum, value )
• ERROR_EVENT ( datum, error )

Datum

Datum extends EventEmitter.

new Datum( value )

Sets the value.

bool hasValue { get; }

Indicates if a value is set.

any value { get; }

Value that is set. Undefined if not set.

any getValue()

Value that is set. Throws NO VALUE DatumError if not set.

any getValueOrDefault( any defaultValue )

Value that is set. Returns defaultValue if not set.

MutableDatum

MutableDatum extends Datum. Provides the ability to change the value.

• Emits SET_EVENT when value is set.
• Emits CHANGE_EVENT when value is changed. Only actually changes if differs.
• Emits ERROR_EVENT when an error happens but is caught.

new MutableDatum( value )

Sets an intial value.

any value { get; set; }

Value that is set. Undefined if not set.

this clearValue()

Clears the set value. When cleared hasValue is false. Returns itself.

this setValue( any value )

Sets the value. Returns itself.

RefreshableDatum

RefreshableDatum extends MutableDatum. Provides the ability to update with a refresh function. Trying to set, clear, or refresh while a refresh is pending will throw PENDING REFRESH DatumError.

• Emits SET_EVENT when value is set.
• Emits CHANGE_EVENT when value is changed. Only actually changes if differs.
• Emits ERROR_EVENT when an error happens but is caught.

new RefreshableDatum( refreshFunction, value )

Sets an initial value and registers a function to be used in refreshing.

bool pendingRefresh { get; }

Indicates if a refresh is in progress.

this refreshValue()

Runs the refresh function and updates the value. Returns itself.

refresh function

any refreshFunction ( RefreshableDatum datum )

Refresh function will be used to update the value of a RefreshableDatum. The return value will be set as the new value of the datum. If an error is thrown then an ERROR_EVENT will be emitted by the datum. If the return value is a promise then will try to resolve it.

DatumError

DatumError extends Error.

• NO VALUE
• PENDING REFRESH

error original { get; }

If wrapping another error then the original error. Otherwise undefined.

Example

const RefreshableDatum = require('datem').RefreshableDatum;
const CHANGE_EVENT = require('datem').CHANGE_EVENT;

function refreshFunction( selfDatum ) {
 return selfDatum.value + 1;
}

let datum = new RefreshableDatum( refreshFunction, 123 );
datum.on( CHANGE_EVENT,
 ( selfDatum, value ) => {
  console.log ( selfDatum.valueOf(), value );
  // { hasValue: bool, value: value } value
 }
);
datum.value = 100;
datum.refreshValue();

License

ISC