@cdellacqua/signals/dist/index.es.js

A simple signal pattern implementation that enables reactive programming

function deriveSignal(signal$, transform) {
  const base$ = makeSignal();
  const emitTransformed = (data) => {
    base$.emit(transform(data));
  };
  const handleUnsubscribe = () => {
    if (unsubscribeOriginal && base$.nOfSubscriptions() === 0) {
      unsubscribeOriginal();
      unsubscribeOriginal = null;
    }
  };
  let unsubscribeOriginal = null;
  return {
    nOfSubscriptions: base$.nOfSubscriptions,
    subscribe: (s) => {
      const unsubscribe = base$.subscribe(s);
      if (!unsubscribeOriginal) {
        unsubscribeOriginal = signal$.subscribe(emitTransformed);
      }
      return () => {
        unsubscribe();
        handleUnsubscribe();
      };
    },
    subscribeOnce: (s) => {
      const unsubscribe = base$.subscribeOnce((v) => {
        s(v);
        handleUnsubscribe();
      });
      if (!unsubscribeOriginal) {
        unsubscribeOriginal = signal$.subscribe(emitTransformed);
      }
      return () => {
        unsubscribe();
        handleUnsubscribe();
      };
    }
  };
}
function coalesceSignals(signals$) {
  const base$ = makeSignal();
  const emit = (data) => {
    base$.emit(data);
  };
  const handleUnsubscribe = () => {
    if (unsubscribeOriginals && base$.nOfSubscriptions() === 0) {
      unsubscribeOriginals.forEach((unsub) => unsub());
      unsubscribeOriginals = null;
    }
  };
  let unsubscribeOriginals = null;
  return {
    nOfSubscriptions: base$.nOfSubscriptions,
    subscribe: (s) => {
      const unsubscribe = base$.subscribe(s);
      if (!unsubscribeOriginals) {
        unsubscribeOriginals = signals$.map((signal$) => signal$.subscribe(emit));
      }
      return () => {
        unsubscribe();
        handleUnsubscribe();
      };
    },
    subscribeOnce: (s) => {
      const unsubscribe = base$.subscribeOnce((v) => {
        s(v);
        handleUnsubscribe();
      });
      if (!unsubscribeOriginals) {
        unsubscribeOriginals = signals$.map((signal$) => signal$.subscribe(emit));
      }
      return () => {
        unsubscribe();
        handleUnsubscribe();
      };
    }
  };
}
function makeSignal() {
  const subscribers = [];
  function emit(v) {
    if (subscribers.length === 0) {
      return;
    }
    for (const subscriber of subscribers.slice()) {
      subscriber(v);
    }
  }
  function unsubscribe(subscriber) {
    const index = subscribers.indexOf(subscriber);
    if (index !== -1) {
      subscribers.splice(index, 1);
    }
  }
  function subscribe(subscriber) {
    const index = subscribers.indexOf(subscriber);
    if (index === -1) {
      subscribers.push(subscriber);
    }
    return () => unsubscribe(subscriber);
  }
  function subscribeOnce(subscriber) {
    const unsubscribeWrapper = subscribe((v) => {
      unsubscribeWrapper();
      subscriber(v);
    });
    return unsubscribeWrapper;
  }
  return {
    emit,
    subscribe,
    subscribeOnce,
    nOfSubscriptions() {
      return subscribers.length;
    }
  };
}
export { coalesceSignals, deriveSignal, makeSignal };