Getting 'sharredString's when trying to parse XSLX in the streaming mode

Sometimes, when I'm trying to use https://github.com/guyonroche/exceljs#reading-xlsx for reading rows in the streaming mode, instead of list of values, I'm getting a list of 'sharredString's

[
   { sharedString: 1 },
   { sharedString: 2 },
   { sharedString: 3 },
   ....
]

I noticed that there is a place when the library is trying to parse sharedString section https://github.com/guyonroche/exceljs/blob/master/lib/stream/xlsx/workbook-reader.js#L84 but looks like it doesn't map them back to row values.

Is it defined behaviour?