/
max_by.ts
61 lines (57 loc) · 1.56 KB
/
max_by.ts
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// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
/**
* Returns the first element that is the largest value of the given function or undefined if there are no elements.
*
* Example:
*
* ```ts
* import { maxBy } from "https://deno.land/std@$STD_VERSION/collections/mod.ts";
* import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
*
* const people = [
* { name: 'Anna', age: 34 },
* { name: 'Kim', age: 42 },
* { name: 'John', age: 23 },
* ];
*
* const personWithMaxAge = maxBy(people, i => i.age);
*
* assertEquals(personWithMaxAge, { name: 'Kim', age: 42 });
* ```
*/
export function maxBy<T>(
array: readonly T[],
selector: (el: T) => number,
): T | undefined;
export function maxBy<T>(
array: readonly T[],
selector: (el: T) => string,
): T | undefined;
export function maxBy<T>(
array: readonly T[],
selector: (el: T) => bigint,
): T | undefined;
export function maxBy<T>(
array: readonly T[],
selector: (el: T) => Date,
): T | undefined;
export function maxBy<T>(
array: readonly T[],
selector:
| ((el: T) => number)
| ((el: T) => string)
| ((el: T) => bigint)
| ((el: T) => Date),
): T | undefined {
let max: T | undefined = undefined;
let maxValue: ReturnType<typeof selector> | undefined = undefined;
for (const current of array) {
const currentValue = selector(current);
if (maxValue === undefined || currentValue > maxValue) {
max = current;
maxValue = currentValue;
}
}
return max;
}