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Learn RxJS
last
signature: last(predicate: function): Observable
last(predicate: function): ObservableEmit the last value emitted from source on completion, based on provided expression.
Examples
Example 1: Last value in sequence
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// RxJS v6+
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import { from } from 'rxjs';
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import { last } from 'rxjs/operators';
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const source = from([1, 2, 3, 4, 5]);
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//no arguments, emit last value
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const example = source.pipe(last());
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//output: "Last value: 5"
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const subscribe = example.subscribe(val => console.log(`Last value: ${val}`));
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Example 2: Last value to pass predicate
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// RxJS v6+
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import { from } from 'rxjs';
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import { last } from 'rxjs/operators';
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const source = from([1, 2, 3, 4, 5]);
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//emit last even number
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const exampleTwo = source.pipe(last(num => num % 2 === 0));
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//output: "Last to pass test: 4"
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const subscribeTwo = exampleTwo.subscribe(val =>
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console.log(`Last to pass test: ${val}`)
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);
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Example 3: Last with default value
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// RxJS v6+
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import { from } from 'rxjs';
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import { last } from 'rxjs/operators';
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const source = from([1, 2, 3, 4, 5]);
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//no values will pass given predicate, emit default
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const exampleTwo = source.pipe(last(v => v > 5, 'Nothing!'));
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//output: 'Nothing!'
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const subscribeTwo = exampleTwo.subscribe(val => console.log(val));
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Additional Resources
- 🎥 💵 - André Staltz
Last modified 1yr ago