Potential issues when adding worksheets across workbooks: Understanding storage differences between SpreadJS and Excel

In this article we will talk about a common scenario: You want to generate a single PDF by combining multiple .sjs files where each file contains just one worksheet. A typical approach might be to load each .sjs file into a SpreadJS instance, then add each sheet to another Spread instance that’s used to export the final PDF. 

At first glance, this might seem like a reasonable solution, but it actually introduces a serious issue. 

async function prepareReportData(blob) {
    try {
        let exportWorkbook = new GC.Spread.Sheets.Workbook(); // Create a new workbook for exporting
        exportWorkbook.removeSheet(0);

        let importWorkbook = new GC.Spread.Sheets.Workbook(); // Temporary workbook for opening the file

        await new Promise((resolve, reject) => {
            importWorkbook.open(blob, () => { // Open the file in the temporary workbook
                var activeSheet = importWorkbook.getActiveSheet();
                
                exportWorkbook.addSheet(0, activeSheet); // Adding the active sheet directly 

                resolve();
            }, (error) => {
                console.error(error);
                reject(error);
            });
        });

        return exportWorkbook; // Return the prepared workbook for PDF export
    } catch (err) {
        console.error("Failed to generate export data:", err);
        throw err;
    }
}