焦点不在input或textarea中，屏蔽回格按钮

if(document.addEventListener){
	document.addEventListener('keydown',backSpaceSearch,false);
}else{
	document.attachEvent('onkeydown',backSpaceSearch)
}
function backSpaceSearch(event){	
	var event=event?event:window.event;
	if(event.keyCode==8){
		var myTarget=event.target || event.srcElement;
		if(myTarget.tagName.toLowerCase()=='input' || myTarget.tagName.toLowerCase()=='textarea'){
			return;
		}else{			
			if(event.preventDefault){
				event.preventDefault();
			}else{
				event.returnValue=false;
			}
		}
	}
}