前端js如何生成一个对象，并转化为json字符串

<script type="text/javascript">
        window.onload = function () {
            var json = [];
            for (var i = 1; i < 5; i++) {
                var j = {};
                j.name = "name";
                j.cars = "22";
                j.obj = i;
                json.push(j);
            }
            var a = JSON.stringify(json);
            alert(a);
        }
    </script>