ie 跟 firefox ff 兼容键盘事件 _Web前端

ie 和 firefox ff 兼容键盘事件
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 <HEAD>
  <TITLE> New Document </TITLE>
  <meta http-equiv=Content-Type content="text/html; charset=utf-8">
  <META NAME="Generator" CONTENT="EditPlus">
  <META NAME="Author" CONTENT="">
  <META NAME="Keywords" CONTENT="">
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    <script language="javascript">
    <!--
        document.onkeydown = function( event_e ){
            if( window.event )
                event_e = window.event;
            var int_keycode = event_e.charCode||event_e.keyCode;
            if( int_keycode == '37' )
                alert( 'left' );
            if( int_keycode == '39' )
                alert( 'right' );
        }
    //-->
    </SCRIPT>
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