Javascript - Return an array consisting of the largest number from each provided sub-array

largest.js

function largest(arr) {
	return arr.map(function(val){
    	return val.reduce(function(prev, current){
        	return current > prev ? current : prev;
        });
    });
}

console.log(largest([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]));