js实现页面加载后自动刷新一次,仅一次

<script>
String.prototype.queryString = function(name) {
var reg = new RegExp("[?&]" + name + "=([^&]+)", "i"),
    r = this.match(reg);
    return r !== null ? unescape(r[1]) : null
};
window.onload = function() {
    var last = location.href.queryString("_v");
    if (location.href.indexOf("?") == -1) {
        location.href = location.href + "?_v=" + (new Date().getTime())
    } else {
        var now = new Date().getTime();
        if (!last) {
            location.href = location.href + "&_v=" + (new Date().getTime())
        } else if (parseInt(last) < (now - 500)) {
            location.href = location.href.replace("_v=" + last, "_v=" + (new Date().getTime()))
        }
    }
};
</script>