Hi Yongguo,

Although it's hidden in the UI by default, LSID is just one of the standard columns that's available on a dataset. There are a number of different ways to get its value. For example, you can request it by using LABKEY.Query.selectRows() and using the "columns" config property. You can use the filterArray config property to filter to the ParticipantId and SequenceNum or Date field (depending on if you have a visit-based or date-based study) so that you get only the row that you're interested in updating.

https://www.labkey.org/download/clientapi_docs/javascript-api/symbols/LABKEY.Query.html#.selectRows

Thanks,
Josh