Import xlsx file using jspreadsheet gives Invalid HTML: could not find <table> error

Question

I'm trying to use jspreadsheet from bossanova.uk to import a .xlsx file as described here. However I get an Invalid HTML: could not find <table> error. This error should mean the file is interpreted as HTML, but it's actually an xlsx file. I created an HTML input allowing the user to choose the file and a container for the spreadsheet:

<input type="file" id="inputXlsFile" />
<div id="spreadsheet"></div>

Then in Javascript:

inputElement = document.getElementById("inputXlsFile");
inputElement.addEventListener("change", handleFiles, false);

var handleFiles = function() {
    const files = this.files;

    jexcel.fromSpreadsheet(files[0], function(result) {
        if (!result.length) {
            console.error('Jspreadsheet: Something went wrong.');
        } else {
            if (result.length == 1) {
                jexcel(document.getElementById('spreadsheet'), result[0]);
            } else {
                jexcel.createTabs(document.getElementById('spreadsheet'), result);
            }
        }
    });
}

Here is a screenshot of the xlsx file opened in Excel: