diff --git a/djx/src/main/ts/observable.ts b/djx/src/main/ts/observable.ts
--- a/djx/src/main/ts/observable.ts
+++ b/djx/src/main/ts/observable.ts
@@ -1,67 +1,10 @@
 import { id as mid} from "module";
 import { Cancellation } from "@implab/core-amd/Cancellation";
-import { ICancellation } from "@implab/core-amd/interfaces";
 import { TraceSource } from "@implab/core-amd/log/TraceSource";
 import { isPromise } from "@implab/core-amd/safe";
-
-const trace = TraceSource.get(mid);
-
-/**
- * The interface for the consumer of an observable sequence
- */
-export interface Observer<T> {
-    /**
-     * Called for the next element in the sequence
-     */
-    next?(value: T): void;
-
-    /**
-     * Called once when the error occurs in the sequence.
-     */
-    error?(e: unknown): void;
-
-    /**
-     * Called once at the end of the sequence.
-     */
-    complete?(): void;
-}
+import { Unsubscribable, Observer, Producer, FusedSink, FusedProducer, AccumulatorFn, Observable, OperatorFn, Subscribable } from "./observable/interfaces";
 
-/**
- * The group of functions to feed an observable. These methods are provided to
- * the producer to generate a stream of events.
- */
-export type Sink<T> = {
-    /**
-     * Call to send the next element in the sequence
-     */
-    next: (value: T) => void;
 
-    /**
-     * Call to notify about the error occurred in the sequence.
-     */
-    error: (e: unknown) => void;
-
-    /**
-     * Call to signal the end of the sequence.
-     */
-    complete: () => void;
-
-    /**
-     * Checks whether the sink is accepting new elements. It's safe to
-     * send elements to the closed sink.
-     */
-    isClosed: () => boolean;
-};
-
-export type Producer<T> = (sink: Sink<T>) => (void | (() => void));
-
-type FusedSink<T> = Omit<Sink<T>, "isClosed">;
-
-type FusedProducer<T> = (sink: FusedSink<T>) => (void | (() => void));
-
-export interface Unsubscribable {
-    unsubscribe(): void;
-}
 
 export const isUnsubscribable = (v: unknown): v is Unsubscribable =>
     v !== null && v !== undefined && typeof (v as Unsubscribable).unsubscribe === "function";
@@ -69,104 +12,11 @@ export const isUnsubscribable = (v: unkn
 export const isSubscribable = <T = unknown>(v: unknown): v is Subscribable<T> =>
     v !== null && v !== undefined && typeof (v as Subscribable<unknown>).subscribe === "function";
 
-export interface Subscribable<T> {
-    /** Subscribes a consumer to events. If a consumer isn't specified
-     * this method activates the producer to achieve side affects if any.
-     */
-    subscribe(consumer?: Observer<T>): Unsubscribable;
-}
 
-export type AccumulatorFn<T, A> = (acc: A, value: T) => A;
-
-export type OperatorFn<T, U> = (source: Observable<T>) => Observable<U>;
-
-/** The observable source of items. */
-export interface Observable<T> extends Subscribable<T> {
-    /** Transforms elements of the sequence with the specified mapper
-     * 
-     * @param mapper The mapper used to transform the values
-     */
-    map<T2>(mapper: (value: T) => T2): Observable<T2>;
-
-    /** Injects the specified observer into the each producer to consumer chain.
-     * The method is used to add side effect to the events processing.
-     * 
-     * @param observer The consumer for the events
-     */
-    tap(observer: Observer<T>): Observable<T>;
-
-    /** Filters elements of the sequence. The resulting sequence will
-     * contain only elements which match the specified predicate.
-     * 
-     * @param predicate The filter predicate.
-     */
-    filter(predicate: (value: T) => boolean): Observable<T>;
-
-    /** Completes the sequence once the condition is met.
-     * @param predicate The condition which should be met to complete the sequence
-     */
-    until(predicate: (value: T) => boolean): Observable<T>;
-
-    /** Keeps the sequence running while elements satisfy the condition.
-     * 
-     * @param predicate The condition which should be met to continue.
-     */
-    while(predicate: (value: T) => boolean): Observable<T>;
-
-    /** Applies accumulator to each value in the sequence and
-     * emits the accumulated value for each source element
-     * 
-     * @param accumulator 
-     * @param initial 
-     */
-    scan<A>(accumulator: AccumulatorFn<T, A>, initial: A): Observable<A>;
-    scan(accumulator: AccumulatorFn<T, T>): Observable<T>;
-
-    /** Applies accumulator to each value in the sequence and
-     * emits the accumulated value at the end of the sequence
-     * 
-     * @param accumulator 
-     * @param initial 
-     */
-    reduce<A>(accumulator: AccumulatorFn<T, A>, initial: A): Observable<A>;
-    reduce(accumulator: AccumulatorFn<T, T>): Observable<T>;
-
-    /** Concatenates the specified sequences with this observable
-     * 
-     * @param seq sequences to concatenate with the current observable
-     * 
-     * The concatenation doesn't accumulate values from the specified sequences,
-     * The result of the concatenation is the new observable which will switch
-     * to the next observable after the previous one completes. Values emitted
-     * before the next observable being active are lost.
-     */
-    cat(...seq: Subscribable<T>[]): Observable<T>;
-
-
-    /** Pipes the specified operator to produce the new observable
-     * @param op The operator consumes this observable and produces a new one
-     * 
-     * The operator is a higher order function which takes a source observable
-     * and returns a producer for the new observable.
-     * 
-     * This function can be used to create a complex mapping between source and
-     * resulting observables. The operator may have a state (or a side effect)
-     * and can be connected to multiple observables.
-     */
-    pipe<U>(op: OperatorFn<T, U>): Observable<U>;
-
-    /** Waits for the next event to occur and returns a promise for the next value
-     * @param ct Cancellation token
-    */
-    next(ct?: ICancellation): Promise<T>;
-
-    /** Collects items of the sequence to the array. */
-    collect(ct?: ICancellation): Promise<T[]>;
-}
 
 const noop = () => { };
 
-const errorFallback = (e: unknown) => trace.error("Unhandled observable error: {0}", e);
+
 
 const sink = <T>(consumer: Observer<T>) => {
     // eslint-disable-next-line @typescript-eslint/unbound-method
diff --git a/djx/src/main/ts/observable/ObservableImpl.ts b/djx/src/main/ts/observable/ObservableImpl.ts
new file mode 100644
--- /dev/null
+++ b/djx/src/main/ts/observable/ObservableImpl.ts
@@ -0,0 +1,169 @@
+import { id as mid } from "module";
+import { AccumulatorFn, FusedProducer, Observable, Observer, OperatorFn } from "./interfaces";
+import { TraceSource } from "@implab/core-amd/log/TraceSource";
+import { scan } from "dojo/parser";
+import { filter } from "dojo/query";
+
+const trace = TraceSource.get(mid);
+
+const noop = () => { };
+
+const errorFallback = (e: unknown) => trace.error("Unhandled observable error: {0}", e);
+
+const sink = <T>(consumer: Observer<T>) => {
+    // eslint-disable-next-line @typescript-eslint/unbound-method
+    const { next, error, complete } = consumer;
+    return {
+        next: next ? next.bind(consumer) : noop,
+        error: error ? error.bind(consumer) : errorFallback, // report unhandled errors
+        complete: complete ? complete.bind(consumer) : noop
+    };
+};
+
+const
+
+export class ObservableImpl<T> implements Observable<T> {
+
+    private readonly _producer: FusedProducer<T>;
+
+    constructor(producer: FusedProducer<T>) {
+        this._producer = producer;
+    }
+
+    subscribe(consumer: Observer<T> = {}) {
+        return {
+            unsubscribe: this._producer(sink(consumer)) ?? noop
+        }
+    }
+
+    map<T2>(mapper: (value: T) => T2) {
+        return new ObservableImpl<T2>(({ next, ...rest }) =>
+            this._producer({
+                next: next !== noop ? (v: T) => next(mapper(v)) : noop,
+                ...rest
+            }));
+    }
+
+    tap({ next: tapNext, complete: tapComplete, error: tapError }: Observer<T>) {
+        return new ObservableImpl<T>(({ next, complete, error }) =>
+            this._producer({
+                next: tapNext ? (v => (tapNext(v), next(v))) : next,
+                complete: tapComplete ? (() => (tapComplete(), complete())) : complete,
+                error: tapError ? (e => (tapError(e), error(e))) : error
+            }));
+    }
+
+    filter: (predicate) => _observe(({ next, ...rest }) =>
+        producer({
+            next: next !== noop ? (v: T) => predicate(v) ? next(v) : void (0) : noop,
+            ...rest
+        })
+    ),
+
+until: predicate => _observe(({ next, complete, ...rest }) =>
+    producer({
+        next: v => predicate(v) ? complete() : next(v),
+        complete,
+        ...rest
+    })
+),
+
+    while: predicate => _observe(({ next, complete, ...rest }) =>
+    producer({
+        next: v => predicate(v) ? next(v) : complete(),
+        complete,
+        ...rest
+    })
+),
+
+    scan: <A>(...args: [AccumulatorFn<T, A>, A] | [AccumulatorFn<T, T>]) => _observe<T | A>(({ next, ...rest }) => {
+        if (args.length === 1) {
+            const [accumulator] = args;
+            let _acc: T;
+            let index = 0;
+            return producer({
+                next: next !== noop ? (v: T) => next(index++ === 0 ? _acc = v : _acc = accumulator(_acc, v)) : noop,
+                ...rest
+            });
+        } else {
+            const [accumulator, initial] = args;
+            let _acc = initial;
+            return producer({
+                next: next !== noop ? (v: T) => next(_acc = accumulator(_acc, v)) : noop,
+                ...rest
+            });
+        }
+    }),
+
+        reduce: <A>(...args: [AccumulatorFn<T, A>, A] | [AccumulatorFn<T, T>]) => _observe<T | A>(({ next, complete, error }) => {
+            if (args.length === 1) {
+                const [accumulator] = args;
+                let _acc: T;
+                let index = 0;
+                return producer({
+                    next: next !== noop ? (v: T) => {
+                        _acc = index++ === 0 ? v : accumulator(_acc, v);
+                    } : noop,
+                    complete: () => {
+                        if (index === 0) {
+                            error(new Error("The sequence can't be empty"));
+                        } else {
+                            next(_acc);
+                            complete();
+                        }
+                    },
+                    error
+                });
+            } else {
+                const [accumulator, initial] = args;
+                let _acc = initial;
+                return producer({
+                    next: next !== noop ? (v: T) => {
+                        _acc = accumulator(_acc, v);
+                    } : noop,
+                    complete: () => {
+                        next(_acc);
+                        complete();
+                    },
+                    error
+                });
+            }
+        }),
+
+            cat: (...seq) => _observe(({ next, complete: final, ...rest }) => {
+                let cleanup: () => void;
+                const len = seq.length;
+                const complete = (i: number) => i < len ?
+                    () => {
+                        const subscription = seq[i].subscribe({ next, complete: complete(i + 1), ...rest });
+                        cleanup = subscription.unsubscribe.bind(subscription);
+                    } : final;
+
+                cleanup = producer({ next, complete: complete(0), ...rest }) ?? noop;
+
+                return () => cleanup();
+            }),
+
+                pipe: <U>(op: OperatorFn<T, U>) => op(_observe(producer)),
+
+                    next: collect(
+                        producer,
+                        ({ next, complete, error }) => ({
+                            next: v => (next(v), complete()),
+                            complete: () => error(new Error("The sequence is empty")),
+                            error
+                        })
+                    ),
+
+                        collect: collect(
+                            producer,
+                            ({ next, complete, error }) => {
+                                const data: T[] = [];
+                                return {
+                                    next: v => data.push(v),
+                                    complete: () => (next(data), complete()),
+                                    error
+                                };
+                            }
+                        )
+}
\ No newline at end of file
diff --git a/djx/src/main/ts/observable/interfaces.d.ts b/djx/src/main/ts/observable/interfaces.d.ts
new file mode 100644
--- /dev/null
+++ b/djx/src/main/ts/observable/interfaces.d.ts
@@ -0,0 +1,153 @@
+import { ICancellation } from "@implab/core-amd/interfaces";
+
+/**
+ * The interface for the consumer of an observable sequence
+ */
+export interface Observer<T> {
+    /**
+     * Called for the next element in the sequence
+     */
+    next?(value: T): void;
+
+    /**
+     * Called once when the error occurs in the sequence.
+     */
+    error?(e: unknown): void;
+
+    /**
+     * Called once at the end of the sequence.
+     */
+    complete?(): void;
+}
+
+/**
+ * The group of functions to feed an observable. These methods are provided to
+ * the producer to generate a stream of events.
+ */
+export type Sink<T> = {
+    /**
+     * Call to send the next element in the sequence
+     */
+    next: (value: T) => void;
+
+    /**
+     * Call to notify about the error occurred in the sequence.
+     */
+    error: (e: unknown) => void;
+
+    /**
+     * Call to signal the end of the sequence.
+     */
+    complete: () => void;
+
+    /**
+     * Checks whether the sink is accepting new elements. It's safe to
+     * send elements to the closed sink.
+     */
+    isClosed: () => boolean;
+};
+
+export type Producer<T> = (sink: Sink<T>) => (void | (() => void));
+
+export type FusedSink<T> = Omit<Sink<T>, "isClosed">;
+
+export type FusedProducer<T> = (sink: FusedSink<T>) => (void | (() => void));
+
+export interface Unsubscribable {
+    unsubscribe(): void;
+}
+
+export interface Subscribable<T> {
+    /** Subscribes a consumer to events. If a consumer isn't specified
+     * this method activates the producer to achieve side affects if any.
+     */
+    subscribe(consumer?: Observer<T>): Unsubscribable;
+}
+
+export type AccumulatorFn<T, A> = (acc: A, value: T) => A;
+
+export type OperatorFn<T, U> = (source: Observable<T>) => Observable<U>;
+
+/** The observable source of items. */
+export interface Observable<T> extends Subscribable<T> {
+    /** Transforms elements of the sequence with the specified mapper
+     * 
+     * @param mapper The mapper used to transform the values
+     */
+    map<T2>(mapper: (value: T) => T2): Observable<T2>;
+
+    /** Injects the specified observer into the each producer to consumer chain.
+     * The method is used to add side effect to the events processing.
+     * 
+     * @param observer The consumer for the events
+     */
+    tap(observer: Observer<T>): Observable<T>;
+
+    /** Filters elements of the sequence. The resulting sequence will
+     * contain only elements which match the specified predicate.
+     * 
+     * @param predicate The filter predicate.
+     */
+    filter(predicate: (value: T) => boolean): Observable<T>;
+
+    /** Completes the sequence once the condition is met.
+     * @param predicate The condition which should be met to complete the sequence
+     */
+    until(predicate: (value: T) => boolean): Observable<T>;
+
+    /** Keeps the sequence running while elements satisfy the condition.
+     * 
+     * @param predicate The condition which should be met to continue.
+     */
+    while(predicate: (value: T) => boolean): Observable<T>;
+
+    /** Applies accumulator to each value in the sequence and
+     * emits the accumulated value for each source element
+     * 
+     * @param accumulator 
+     * @param initial 
+     */
+    scan<A>(accumulator: AccumulatorFn<T, A>, initial: A): Observable<A>;
+    scan(accumulator: AccumulatorFn<T, T>): Observable<T>;
+
+    /** Applies accumulator to each value in the sequence and
+     * emits the accumulated value at the end of the sequence
+     * 
+     * @param accumulator 
+     * @param initial 
+     */
+    reduce<A>(accumulator: AccumulatorFn<T, A>, initial: A): Observable<A>;
+    reduce(accumulator: AccumulatorFn<T, T>): Observable<T>;
+
+    /** Concatenates the specified sequences with this observable
+     * 
+     * @param seq sequences to concatenate with the current observable
+     * 
+     * The concatenation doesn't accumulate values from the specified sequences,
+     * The result of the concatenation is the new observable which will switch
+     * to the next observable after the previous one completes. Values emitted
+     * before the next observable being active are lost.
+     */
+    cat(...seq: Subscribable<T>[]): Observable<T>;
+
+
+    /** Pipes the specified operator to produce the new observable
+     * @param op The operator consumes this observable and produces a new one
+     * 
+     * The operator is a higher order function which takes a source observable
+     * and returns a producer for the new observable.
+     * 
+     * This function can be used to create a complex mapping between source and
+     * resulting observables. The operator may have a state (or a side effect)
+     * and can be connected to multiple observables.
+     */
+    pipe<U>(op: OperatorFn<T, U>): Observable<U>;
+
+    /** Waits for the next event to occur and returns a promise for the next value
+     * @param ct Cancellation token
+    */
+    next(ct?: ICancellation): Promise<T>;
+
+    /** Collects items of the sequence to the array. */
+    collect(ct?: ICancellation): Promise<T[]>;
+}
\ No newline at end of file
diff --git a/playground/package-lock.json b/playground/package-lock.json
--- a/playground/package-lock.json
+++ b/playground/package-lock.json
@@ -30,6 +30,7 @@
         },
         "../djx/build/npm/package": {
             "name": "@implab/djx",
+            "version": "1.10.0",
             "dev": true,
             "license": "BSD-2-Clause",
             "peerDependencies": {