Get data from Excel file stored in SharePoint using Excel REST API

get-data-from-excel.js

var fileRelativeUrl = "Shared%20Documents/book1.xlsx";
var sheetName = "Sheet1";
var range = "A1|J45";

var url = _spPageContextInfo.webServerRelativeUrl.replace(/\/$/, '') + "/";
loadXMLDoc(url + "_vti_bin/ExcelRest.aspx/" + fileRelativeUrl + "/model/Ranges('" + sheetName + "!" + range + "')?$format=atom", function (text) {
    var parser = new DOMParser();
    var excelRestNS = 'http://schemas.microsoft.com/office/2008/07/excelservices/rest';
    var xmlDoc = parser.parseFromString(text, "text/xml");
    var rows = xmlDoc.getElementsByTagNameNS(excelRestNS, 'row');

    // Get a text from cell A1
    var row = 0;
    var column = 0;
    var cell = rows[row].getElementsByTagNameNS(excelRestNS, 'c')[column];
    var formattedValueElement = cell.getElementsByTagNameNS(excelRestNS, 'fv')[0];
    var cellText = formattedValueElement.childNodes[0].wholeText;
    console.log(cellText);

});

// super simple implementation of XHR, you can alternatively use anything else e.g. $.ajax
function loadXMLDoc(url, callback) {
    var xmlhttp = new XMLHttpRequest();

    xmlhttp.onreadystatechange = function () {
        if (xmlhttp.readyState == XMLHttpRequest.DONE) {
            if (xmlhttp.status == 200) {
                callback(xmlhttp.responseText);
            }
            else {
                console.log('Error ' + xmlhttp.status, xmlhttp);
            }
        }
    };

    xmlhttp.open("GET", url, true);
    xmlhttp.send();
}

Note: it usually fails with error 500 if the workbook is currently open and being edited by you or someone else.