underscore mixins

gistfile1.js

_.mixin({
    /**
     * Iterates over an array of numbers and returns the sum. Example:
     *
     *  var sum = _.sum([1, 2, 3]);
     *  => 6
     *
     * @param obj
     * @returns {Number}
     */
    sum: function (obj) {
        if (!_.isArray(obj) || obj.length == 0) {
            return 0;
        }
        return _.reduce(obj, function (memo, num) {
            return memo + num;
        }, 0);
    },

    /**
     *  var mul = _.mul([1, 2, 3]);
     *  => 6
     *
     * @param obj
     * @returns {Number}
     */
    mul: function (obj) {
        if (!_.isArray(obj) || obj.length == 0) {
            return 0;
        }
        return _.reduce(obj, function (memo, num) {
            return memo * num;
        }, 1);
    },

    /**
     * _.chunk([2,3,4,5], 2);
     * => [[2,3],[4,5]]
     *
     * @param array
     * @param unit
     * @returns {*}
     */
    chunk: function (array, unit) {
        if (!_.isArray(array)) return array;
        unit = Math.abs(unit);
        var results = [],
            length = Math.ceil(array.length / unit);

        for (var i = 0; i < length; i++) {
            results.push(array.slice(i * unit, (i + 1) * unit));
        }
        return results;
    }
});