Convert proxy object to normal object vue JS

I have been trying to convert excel file to Json and the problem is that when I want to add this data to an array in the component’s data , I am unable to do that.
I tried to see what is happening in the console , and the component’s data is changed to proxy object.
here’s my data :

  data(){ 
  return {
    arr: [],
  };
  },

here’s my function :

    onChange(event) {
      var input = event.target;
      var reader = new FileReader();
      reader.readAsBinaryString(input.files[0]);
      reader.onload = () => {
        var fileData = reader.result;
        var wb = XLSX.read(fileData, {type : 'binary'});
        wb.SheetNames.forEach((sheetName) => {
            var rowObj =XLSX.utils.sheet_to_json(wb.Sheets[sheetName]);
            for(const item of rowObj) {
                this.arr.push(item);
          }
        })
        console.log(this.arr);


      }; 

    },

doing console.log(this.arr[1]) or any number outside the onload function will result in an undefined message.