skipIfNoChange (distinctUntilChanged)

Skips emissions if the value hasn’t changed from the previous emission. Uses a custom equality function or Object.is by default.

Marble Diagram

skipIfNoChange()

Example

//  Timeline:
//
//  num$      1     1     2     2     1     2     3     2
//  distinct$ 1           2           1     2     3     2
//
//  Explanation:
//  - skipIfNoChange filters out consecutive duplicate values
//  - Uses strict equality (===) for comparison
//  - Only emits when the value actually changes

const num$ = source<number>();

const distinct$ = num$.pipe(skipIfNoChange());

const valueHistory: number[] = [];

distinct$.subscribe((x) => {
    valueHistory.push(x);
});

num$.next(1); // logs: 1

assert.deepStrictEqual(valueHistory, [1]);

num$.next(1); // nothing logged

assert.deepStrictEqual(valueHistory, [1]);

num$.next(2); // logs: 2

assert.deepStrictEqual(valueHistory, [1, 2]);

num$.next(2); // nothing logged

num$.next(1); // logs: 1

assert.deepStrictEqual(valueHistory, [1, 2, 1]);

num$.next(2); // logs: 2

assert.deepStrictEqual(valueHistory, [1, 2, 1, 2]);

num$.next(3); // logs: 3

assert.deepStrictEqual(valueHistory, [1, 2, 1, 2, 3]);

num$.next(2); // logs: 2

assert.deepStrictEqual(valueHistory, [1, 2, 1, 2, 3, 2]);

View source on GitHub