max.tsā¢1.4 kB
import { reduce } from './reduce';
import { MonoTypeOperatorFunction } from '../types';
import { isFunction } from '../util/isFunction';
/**
* 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.
*
* 
*
* ## Examples
*
* Get the maximal value of a series of numbers
*
* ```ts
* import { of, max } from 'rxjs';
*
* of(5, 4, 7, 2, 8)
* .pipe(max())
* .subscribe(x => console.log(x));
*
* // Outputs
* // 8
* ```
*
* Use a comparer function to get the maximal item
*
* ```ts
* import { of, max } from 'rxjs';
*
* of(
* { age: 7, name: 'Foo' },
* { age: 5, name: 'Bar' },
* { age: 9, name: 'Beer' }
* ).pipe(
* max((a, b) => a.age < b.age ? -1 : 1)
* )
* .subscribe(x => console.log(x.name));
*
* // Outputs
* // 'Beer'
* ```
*
* @see {@link min}
*
* @param comparer Optional comparer function that it will use instead of its
* default to compare the value of two items.
* @return A function that returns an Observable that emits item with the
* largest value.
*/
export function max<T>(comparer?: (x: T, y: T) => number): MonoTypeOperatorFunction<T> {
return reduce(isFunction(comparer) ? (x, y) => (comparer(x, y) > 0 ? x : y) : (x, y) => (x > y ? x : y));
}