data-value的值应该怎么获取

data-value的值应该如何获取？
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C/C++ code

if (m_bFirstLi)    {        m_cstrExternInfo += _T("<li class=\"extern-sel\" data-value=\"");    }    else    {        m_cstrExternInfo += _T("<li class=\"extern-notsel\" data-value=\"");    }    m_bFirstLi = FALSE;    m_cstrExternInfo += cstrMsg;    m_cstrExternInfo += _T("\"><a href=\"#\"><span>");    m_cstrExternInfo += cstrMsg;    m_cstrExternInfo += _T("</span></a></li>");

JScript code

var strXML="";    function showNode(dltable) {        for(var i = 0; i < dltable.length; i++)        {            if (dltable[i].nodeType == 1) {                if (dltable[i].nodeName == "dt" || dltable[i].nodeName == "DT") {                    strXML += "<pfield fname=\"";                    strXML += dltable[i].innerHTML;                    strXML += "\" ";                }                if (dltable[i].nodeName == "li" || dltable[i].nodeName == "LI") {                    if(dltable[i].className == "extern-sel"){                        strXML += "fvname=\"";                        strXML += dltable[i].dataset.value;                        strXML += "\" >";                        break;                    }                }                if (dltable[i].childNodes.length > 0) {                    showNode(dltable[i].childNodes);                }           }       }    }        var dltable = document.getElementById("infolist").childNodes;        showNode(dltable);