node_modules/rxjs/src/internal/util/mapOneOrManyArgs.ts

import { OperatorFunction } from "../types";
import { map } from "../operators/map";

const { isArray } = Array;

function callOrApply<T, R>(fn: ((...values: T[]) => R), args: T|T[]): R {
    return isArray(args) ? fn(...args) : fn(args);
}

/**
 * Used in several -- mostly deprecated -- situations where we need to 
 * apply a list of arguments or a single argument to a result selector.
 */
export function mapOneOrManyArgs<T, R>(fn: ((...values: T[]) => R)): OperatorFunction<T|T[], R> {
    return map(args => callOrApply(fn, args))
}