last.md

#last

signature: last(predicate: function): Observable

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

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💡 The counterpart to last is first!

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Examples

Example 1: Last value in sequence

( jsBin | jsFiddle )

import { from } from 'rxjs/observable/from';
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

( jsBin | jsFiddle )

import { from } from 'rxjs/observable/from';
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 result selector

( jsBin | jsFiddle )

import { from } from 'rxjs/observable/from';
import { last } from 'rxjs/operators';

const source = from([1, 2, 3, 4, 5]);
//supply an option projection function for the second parameter
const exampleTwo = source.pipe(
  last(
    v => v > 4,
    v => `The highest emitted number was ${v}`
  )
);
//output: 'The highest emitted number was 5'
const subscribeTwo = exampleTwo.subscribe(val => console.log(val));

Example 4: Last with default value

( jsBin | jsFiddle )

import { from } from 'rxjs/observable/from';
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, v => v, 'Nothing!'));
//output: 'Nothing!'
const subscribeTwo = exampleTwo.subscribe(val => console.log(val));

Additional Resources

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

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