last

연산자(operator) 정의: 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

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

Example 2: Last value to pass predicate

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const source = Rx.Observable.from([1,2,3,4,5]);
//emit last even number
const exampleTwo = source.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

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const source = Rx.Observable.from([1,2,3,4,5]);
//supply an option projection function for the second parameter
const exampleTwo = source.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

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const source = Rx.Observable.from([1,2,3,4,5]);
//no values will pass given predicate, emit default
const exampleTwo = source.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

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