jquery阻止用户点Backspace返回上一页

$(document).keydown(function(e){   var target = e.target ;   var tag = e.target.tagName.toUpperCase();   if(e.keyCode == 8){    if((tag == 'INPUT' && !$(target).attr("readonly"))||(tag == 'TEXTAREA' && !$(target).attr("readonly"))){     if((target.type.toUpperCase() == "RADIO") || (target.type.toUpperCase() == "CHECKBOX")){      return false ;     }else{      return true ;      }    }else{     return false ;    }   }  });

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