回调函数在从另一个文件中的函数调用时返回未定义的值

Question

I'm new to javascript/nodeJS programming. I want to read a cell value from excel file which I am able to do using excelJS API and I need to return this cell value to a function in anothor file. since it's an asynchronous operation I am using callbacks to handle it but somehow callback function is returning undefined value. I am unable to fix it even after trying so hard. It would be a great help for me If someone provides me with a solution. I have two .js files, first is readvalues.js file and other is mycallback.js file. I am calling mycallback function from readvalue function which is in another file with three parameters(first is sheetName, second is ColumnName, third is callback function). when I print the value received from mycallback function it is showing undefined. Below is the code snippet:

readvalus.js

var mycallback = require('./mycallback.js');        
var Excel = require('exceljs'); 
function readvalues(){
    console.log('Calling mycallback Function');
    mycallback('General Data', 'Name', function(name){
        console.log('Received name from mycallback function = ' +name); //displays value of name as undefined
    }); 
    console.log('Finished calling mycallback Function');
}
readvalues();

mycallback function (which internally calls another function called getData).

var Excel = require('exceljs');
var mycallback = function(sheetName, columnName,callbackOne) {
    getData(sheetName, columnName, function(value){
        console.log('Data received from getData Function = '+value); //prints value as undefined.
        callbackOne(value);
    }); 
}

function getData(sheetName, columnName, callbackTwo){
    var workbook = new Excel.Workbook();
    var filename = './data.xlsx';
    workbook.xlsx.readFile(filename) //function of exceljs API
    .then(function(){
    var worksheet = workbook.getWorksheet(sheetName);
    var row = worksheet.getRow(1).values;
    for(var i=1; i<row.length; i++){
        if(row[i] === columnName){
            var rowVal = worksheet.getRow(2).values;
            var data = rowVal[i];
        }
    }
    console.log('Data passed from getData Function = '+data);   //prints value of data as undefined.
    callbackTwo(data);
    }) 
}
module.exports = mycallback;

Note: When I run mycallback function (like mycallback('Common Data', 'Name') without callbackOne in mycallback function) individually it is printing expected value "John" perfectly.

Outputs:

Outputs

Excel Data Data which I want to read from the excel

Answer 1

将“常规数据”替换为readvalus.js中的“公共数据”