last

signature: last(predicate: function): Observable

Emit the last value emitted from source on completion, based on provided expression.

The counterpart to last is first!

Examples

Example 1: Last value in sequence

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { from } from 'rxjs';
import { last } from 'rxjs/operators';

const source = from([1, 2, 3, 4, 5]);
//no arguments, emit last value
const example = source.pipe(last());
//output: "Last value: 5"
const subscribe = example.subscribe(val => console.log(`Last value: ${val}`));

Example 2: Last value to pass predicate

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { from } from 'rxjs';
import { last } from 'rxjs/operators';

const source = from([1, 2, 3, 4, 5]);
//emit last even number
const exampleTwo = source.pipe(last(num => num % 2 === 0));
//output: "Last to pass test: 4"
const subscribeTwo = exampleTwo.subscribe(val =>
  console.log(`Last to pass test: ${val}`)
);

Example 3: Last with default value

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { from } from 'rxjs';
import { last } from 'rxjs/operators';

const source = from([1, 2, 3, 4, 5]);
//no values will pass given predicate, emit default
const exampleTwo = source.pipe(last(v => v > 5, 'Nothing!'));
//output: 'Nothing!'
const subscribeTwo = exampleTwo.subscribe(val => console.log(val));

Additional Resources

• last - Official docs
• Filtering operator: takeLast, last - André Staltz

Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/last.ts