Operators

Operators are small functions that take a source observable and return a new one. You apply them with pipe. Each operator subscribes to its source, transforms the notifications, and forwards them to its own observer. Errors thrown inside an operator callback are routed to the observer's error handler.

import { Observable, map, filter, distinctUntilChanged, tap } from '@remotex-labs/xobservable';

map

Projects each value through a function.

const doubled = numbers.pipe(map((x) => x * 2));

Parameter	Description
project	Transforms each source value into output.

If project throws, the error is routed to error and that value is not emitted.

filter

Emits only the values that satisfy a predicate; non-matching values are dropped.

const evens = numbers.pipe(filter((x) => x % 2 === 0));

Parameter	Description
predicate	Returns true to emit the value, false to drop it.

distinctUntilChanged

Emits a value only when it differs from the previously emitted one. The first value always passes through.

// Default strict equality
source.pipe(distinctUntilChanged());

// Compare by a field
users.pipe(distinctUntilChanged((prev, curr) => prev.id === curr.id));

Parameter	Default	Description
compareFn	(a, b) => a === b	Returns true when two values are considered equal.

tap

Runs a side effect for each value and forwards the value unchanged. Useful for logging or tracking.

const logged = numbers.pipe(tap((x) => console.log('value', x)));

Parameter	Description
sideEffect	Invoked for each value; its return value is ignored.

If sideEffect throws, the error is routed to error and that value is not emitted.

Composing operators

Operators combine left to right in a single pipe call:

const result = source.pipe(
    filter((x) => x % 2 === 0),
    map((x) => x * 10),
    distinctUntilChanged()
);

See Piping & Composition for how types flow through the chain.