I wrote some code to create arrays of objects in js files based on data in txt files as follows:

var num1 = ['100', '200', '500', '1000']
var num2 = ['10', '20', '30', '40', '50']

for (var i of num1) {
    for (var j of num2) {
        var source = './dat/txt/data_' + i + '_' + j + '.txt'
        var dest = './dat/js/data_' + i + '_' + j + '.js'
        var write = '[\n'
        fs.readFile(source, 'utf-8', function (err, data) {
            if (err) {
                console.log(err)
            }
            var datArray = data.split('\r\n')
            for(let k=0;k<parseInt(i);k++){
                var numbers = datArray[k].split(' ')
                write = write.concat('{\npos:\nx:',numbers[0],',\ny:',numbers[1],'\n},\nbeta:',numbers[2],'\n},')
            }
        })
        fs.writeFile(dest, write, (err) => {
            if (err) {
                console.log(err)
            } else console.log('Written successfully')
        })
    }
}

The txt files have the format as follow:

1 2 3
1 2 3
1 2 3
....

And I want to create Arrays of objects as follow:

[
  {
    pos: {
      x: 1,
      y: 2,
    },
    beta: 3
  },
  ...
]

When I run the code, it has this Error:

var numbers = datArray[k].split(' ')
TypeError: Cannot read properties of undefined (reading 'split')

I tried log the array datArray and it's a normal Array of Strings, and the length of datArray equals value of i. The output files also only write a single character '[' and a line break. What am I doing wrong here?