if the excel sheet is also on the client, and you know the name, you can go activeX:
var xlApp = new ActiveXObject("Excel.Application");
xlApp.visible = true //set this to false if you are sure the whole thing works correctly
xlDoc = xlApp.Open("hereyourfilename");
go on with the excel-instance to read the data, check the vba documentation to find out how to extract the cell data you want.
at the end, close the document and close the excel instance
xlDoc.Close(1); // you should provide some constant here, to prevent excel from asking to save changes i believe its 1
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