S3 Upload with Excel data using Node.js


I am trying to upload an excel file to S3 using Node.js and aws-sdk

The input is JSON and I am using XLSX library to convert it to a workbook and upload to S3 using the below code.

    const wb = XLSX.utils.book_new();

    //Convert JSON to sheet data
    const sheetData = XLSX.utils.json_to_sheet(req.body);
    XLSX.utils.book_append_sheet(wb, sheetData, 'Sheet 1');
    const sheetDataBuffer = XLSX.write(wb, {bookType: 'xlsx', type: 'buffer', bookSST: false});
    const s3 = new AWS.S3();
        Key: file,
        Bucket: <bucket name>,
        Body: sheetDataBuffer,
        ContentType: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
        ContentEncoding: 'base64'
        .then(data => {
            logger.debug("uploaded the data");

However, when I view the uploaded file on S3, it shows garbled/corrupt data. What am I missing? Is this a content encoding issue?

Update: It looks like the client side parsing library I am using — Papaparse — parses the excel content as garbled. I tried setting the encoding option to ‘utf-8’ but it doesn’t help. Any idea what am I missing?

     Papa.parse(e.target.files[0], {
        encoding: 'utf-8',
        download: true,
        complete: async data => {
            // data.data is garbled
            const response = await fetch('/<apipath>', {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json',
                body: data.data
            const res = await response;


So I figured it out using XSLX library on the client side (no longer using Papaparse), in case it helps someone.

    const reader = new FileReader();
    reader.onload = async (evt) => {
        const bstr = evt.target.result;
        const wb = XLSX.read(bstr, {type:'binary'});
        const wsname = wb.SheetNames[0];
        const ws = wb.Sheets[wsname];

        //data is parsed correctly
        const data = XLSX.utils.sheet_to_json(ws, {header:1});
        const response = await fetch('/<apipath>', {
            method: 'POST',
            headers: {
                'Content-Type': 'application/json',
            body: JSON.stringify(data)
        const res = await response;
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