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condition

import { condition } from 'patronum';
// or
import { condition } from 'patronum/condition';

Motivation​

Condition is very similar to guard, but allows you to have else branch along with simple if matcher.

condition({ source: Unit, if: Store, then?: Unit, else?: Unit })​

Formulae​

result = condition({
  source,
  if: $checker,
  then,
  else,
});
  • When source is triggered, check value of $checker, if it equals true, trigger then with value from source, otherwise trigger else with value from source
  • result is the same unit as source allows to nest condition to another condition or sample

Arguments​

  1. source (Unit<T>) — Data from this unit will be passed to then or else
  2. if (Store<boolean>) — Updates of this store will not trigger then and else
  3. then (Unit<T>) — This unit will be triggered with data from source if $checker contains true. Required if else is not provided
  4. else (Unit<T>) — This unit will be triggered with data from source if $checker contains false. Required if then is not provided

Returns​

  1. (Unit<T>) — The same unit type that passed to source

Example​

const change = createEvent();
const $source = createStore('data').on(change, (_, payload) => payload);

const toggle = createEvent();
const $isEnabled = createStore(false).on(toggle, (is) => !is);

const enabled = createEvent();
const disabled = createEvent();

condition({
  source: $source,
  if: $isEnabled,
  then: enabled,
  else: disabled,
});
enabled.watch((payload) => console.log('enabled -', payload));
disabled.watch((payload) => console.log('disabled -', payload));

change('newdata');
// => disabled - newdata

toggle();
change('data');
// => enabled - data

condition({ source: Unit<T>, if: T, then?: Unit, else?: Unit })​

Formulae​

result = condition({
  source,
  if: value,
  then,
  else,
});
  • When source is triggered, compare value literal with source payload, if it equals trigger then with value from source, otherwise trigger else with value from source
  • result is the same unit as source allows to nest condition to another condition or sample

Arguments​

  1. source (Unit<T>) — Data from this unit will be passed to then or else
  2. if (T) — Just value to compare with source payload. Note: objects will be compared by reference
  3. then (Unit<T>) — This unit will be triggered with data from source if $checker contains true. Required if else is not provided
  4. else (Unit<T>) — This unit will be triggered with data from source if $checker contains false. Required if then is not provided

Returns​

  1. (Unit<T>) — The same unit type that passed to source

Example​

const increment = createEvent();
const $source = createStore(0).on(increment, (state) => state + 1);

const log = createEvent();
const run = createEffect().use((data) => {
  console.info('FAKE RUN EFFECT', data);
});

condition({
  source: $source,
  if: 4,
  then: run,
  else: log,
});

log.watch((payload) => console.log('LOG ABOUT IT', payload));

increment(); // => LOG ABOUT IT 1
increment(); // => LOG ABOUT IT 2
increment(); // => LOG ABOUT IT 3
increment(); // => FAKE RUN EFFECT 4
increment(); // => LOG ABOUT IT 5

condition({ source: Unit<T>, if: Function, then?: Unit, else?: Unit })​

Formulae​

result = condition({
  source,
  if: (payload) => boolean,
  then,
  else,
});
  • When source is triggered, call if with source payload, if it returns true trigger then with value from source, otherwise trigger else with value from source
  • result is the same unit as source allows to nest condition to another condition or sample

Arguments​

  1. source (Unit<T>) — Data from this unit will be passed to then or else
  2. if ((payload: T) => boolean) — Function comparator. It should return boolean
  3. then (Unit<T>) — This unit will be triggered with data from source if $checker contains true. Required if else is not provided
  4. else (Unit<T>) — This unit will be triggered with data from source if $checker contains false. Required if then is not provided

Returns​

  1. (Unit<T>) — The same unit type that passed to source

Example​

const change = createEvent();
const $source = createStore('data').on(change, (_, payload) => payload);
const target = createEvent();
const another = createEvent();

condition({
  source: $source,
  if: (source) => source.length > 3,
  then: target,
  else: another,
});
target.watch((payload) => console.log('triggered', payload));
another.watch((payload) => console.log('condition else:', payload));

change('newdata');
// => triggered newdata

change('old');
// => condition else: old

Examples​

Source is event​

const inputChanged = createEvent();
const $value = createStore('');
const $error = createStore(false);

const setError = createEvent();
const setValue = createEvent();

$value.on(setValue, (_, value) => value);
$error.on(setError, () => true).on(setValue, () => false);

condition({
  source: inputChanged,
  if: isValid,
  then: setValue,
  else: setError,
});

function isValid(value) {
  return value.trim().length > 0;
}

Condition can be nested​

const $value = createStore('hello@world');
const updateEmail = createEvent<string>();

condition({
  source: $value,
  if: (length) => length > 0,
  then: condition({
    if: (string) => string.includes('@'),
    then: updateEmail,
  }),
});