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Overview

Skip a specified number of values before the completion of an observable.
skipLast uses a ring buffer to hold values until enough new values have been emitted to know that the buffered values are not part of the last N values.

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Type Signature

function skipLast<T>(skipCount: number): MonoTypeOperatorFunction<T>

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Parameters

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skipCount
number
required
Number of elements to skip from the end of the source Observable.If skipCount <= 0, all values pass through immediately.

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Returns

MonoTypeOperatorFunction<T> - A function that returns an Observable that skips the last count values emitted by the source Observable.

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How It Works

  1. Maintains a ring buffer of size skipCount
  2. For each value:
    • If buffer not full: adds to buffer
    • If buffer full: emits the oldest value and adds new value to buffer
  3. On completion: discards all buffered values (they are the “last N”)
After subscribing, unsubscribing will not result in the emission of the buffered skipped values.

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Usage Examples

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Basic Example

import { of, skipLast } from 'rxjs';

const numbers = of(1, 2, 3, 4, 5);
const skipLastTwo = numbers.pipe(skipLast(2));

skipLastTwo.subscribe(x => console.log(x));

// Output:
// 1
// 2
// 3
// (4 and 5 are skipped)

import { from, skipLast } from 'rxjs';

const csvLines = [
  'Alice,30,NYC',
  'Bob,25,LA',
  'Charlie,35,SF',
  'Total: 3 rows',
  'Generated: 2024-01-01'
];

const dataOnly$ = from(csvLines).pipe(
  skipLast(2) // Skip footer lines
);

dataOnly$.subscribe(line => {
  console.log('Data:', line);
  processDataRow(line);
});

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Remove Closing Elements

import { from, skipLast } from 'rxjs';

const xmlTokens = ['<data>', '<item>A</item>', '<item>B</item>', '</data>'];

const itemsOnly$ = from(xmlTokens).pipe(
  skip(1), // Skip opening tag
  skipLast(1) // Skip closing tag
);

itemsOnly$.subscribe(console.log);
// Output: <item>A</item>, <item>B</item>
  • skip - Skips first N values
  • skipUntil - Skips until another Observable emits
  • skipWhile - Skips while condition is true
  • take - Takes first N values
  • takeLast - Takes last N values