JS屏蔽BackSpace键

if (typeof window.event != 'undefined') {
		  document.onkeydown = function() {
		    var type = event.srcElement.type;
		    var code = event.keyCode;
		    return ((code != 8 && code != 13) ||
		            (type == 'text' && code != 13 ) ||
		            (type == 'textarea') ||
		            (type == 'submit' && code == 13))
		  }
		} else { // FireFox/Others
		  document.onkeypress = function(e) {

		    var type = e.target.localName.toLowerCase();
		    var code = e.keyCode;
		    if ((code != 8 && code != 13) ||
		        (type == 'input' && code != 13 ) ||
		        (type == 'textarea') ||
		        (type == 'submit' && code == 13)) {
		        return true;
		    } else {
		        return false ;
		    }
		  }
		}