es6/operators/max.js
import { reduce } from './reduce';
/**
* The Max operator operates on an Observable that emits numbers (or items that can be compared with a provided function),
* and when source Observable completes it emits a single item: the item with the largest value.
*
* <img src="./img/max.png" width="100%">
*
* @example <caption>Get the maximal value of a series of numbers</caption>
* Rx.Observable.of(5, 4, 7, 2, 8)
* .max()
* .subscribe(x => console.log(x)); // -> 8
*
* @example <caption>Use a comparer function to get the maximal item</caption>
* interface Person {
* age: number,
* name: string
* }
* Observable.of<Person>({age: 7, name: 'Foo'},
* {age: 5, name: 'Bar'},
* {age: 9, name: 'Beer'})
* .max<Person>((a: Person, b: Person) => a.age < b.age ? -1 : 1)
* .subscribe((x: Person) => console.log(x.name)); // -> 'Beer'
* }
*
* @see {@link min}
*
* @param {Function} [comparer] - Optional comparer function that it will use instead of its default to compare the
* value of two items.
* @return {Observable} An Observable that emits item with the largest value.
* @method max
* @owner Observable
*/
export function max(comparer) {
const max = (typeof comparer === 'function')
? (x, y) => comparer(x, y) > 0 ? x : y
: (x, y) => x > y ? x : y;
return reduce(max);
}
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