Array.reduce to maximum value

Using Array.reduce to find the maximum value in an Array.

HTML

<p>Maximum value: <span id="max"></span>

</p>

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JavaScript

(function () {
    'use strict';

    function sum(previous, current) {
        return previous + (current === undefined ? 0: current);
    }

    var data = [{
        v: [1, 3, 4]
    }, {
        v: [7, 6, 5]
    }, {
        v: [9, 10, 1]
    }, {
        v: [3, 8, 2]
    }, {
        v: [2, 7, 8]
    }, {
        v: [11, 5, 6]
    }, {
        v: [6, 3, 1]
    }, {
        v: [4, 2, 1]
    }];

    var maximum = data.reduce(function (previous, current) {
        return Math.max(isNaN(previous) ? previous.v.reduce(sum) : previous, current.v.reduce(sum));
    });

    document.getElementById('max').innerHTML = maximum;
}());