防止input和textarea 浏览器中Backspace仍可用

//防止input和textarea 浏览器中Backspace仍可用  
$(function () {
    $(document).keydown(function (e) {
        var keyEvent;
        if (e.keyCode == 8) {
            var d = e.srcElement || e.target;
            if (d.tagName.toUpperCase() == 'INPUT' || d.tagName.toUpperCase() == 'TEXTAREA') {
                keyEvent = d.readOnly || d.disabled;
            }
        } else {
            keyEvent = false;
        }
        if (keyEvent) {
            e.preventDefault();
        }
    })
});