Some extensions to Sugar.

zegnat.sugar.js

Number.extend({
    'sign': function() {
        // http://stackoverflow.com/a/21294663/3225372
        return typeof this === 'number' ? this ? this < 0 ? -1 : 1 : this === this ? this : NaN : NaN;
    },
    'isPositive': function() {
        return this.sign() === 1;
    },
    'isNegative': function() {
        return this.sign() === -1;
    },
    'isNegativeZero': function() {
        // http://www.wirfs-brock.com/allen/posts/128
        return this ? false : 1/this === -Infinity;
    }
});