禁用backspace网页回退功能的实现代码

<script language="JavaScript">document.onkeydown = check;function check(e) {var code;if (!e) var e = window.event;if (e.keyCode) code = e.keyCode;else if (e.which) code = e.which;if (((event.keyCode == 8) && //BackSpace ((event.srcElement.type != "text" && event.srcElement.type != "textarea" && event.srcElement.type != "password") || event.srcElement.readOnly == true)) || ((event.ctrlKey) && ((event.keyCode == 78) || (event.keyCode == 82)) ) || //CtrlN,CtrlR (event.keyCode == 116) ) { //F5 event.keyCode = 0; event.returnValue = false; }return true;}</script>