PropEr/Quickcheck example in Javascript

gistfile1.js

var Proper = {};

function even_number() {
    return LET([integer()],
        function(i) {
            return i * 2;
        }
    );
}

Proper.props = {
    string_fromCharCode: function() {
        return FORALL([string()],
            function(charlist) {
                var s = String.fromCharCodes(charlist);
                if(typeof s != 'string') {
                    return false;
                }
                var converted = s.toCharCodes();
                for(var i=0; i<charlist.length; i++) {
                    if(charlist[i] != converted[i]) {
                        return false;
                    }
                }
                return charlist.length == converted.length;
            }
        );
    },
    string_reverse: function() {
        return FORALL([string()],
            function(charlist) {
                var s = String.fromCharCodes(charlist);
                var reversed = s.reverse();
                var half = s.length / 2;
                var left = s.substring(0, Math.floor(half));
                var right = s.substring(Math.ceil(half));
                var symetric = left == right;
                return (symetric && reversed == s) || (reversed != s && reversed.reverse() == s);
            }
        );
    },
    even_number: function() {
        return FORALL([even_number()],
            function(i) {
                return i % 2 == 0;
            }
        );
    },
    pos_integer: function() {
        return FORALL([pos_integer()],
            function(i) {
                return i > 0
            }
        );
    },
    neg_integer: function() {
        return FORALL([neg_integer()],
            function(i) {
                return i < 0
            }
        );
    },
    non_neg_integer: function() {
        return FORALL([non_neg_integer()],
            function(i) {
                return i >= 0
            }
        );
    }
};