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How to parse pre-selected excel file into javascript object?

i know there are tonnes of solutions regarding this but no answers for pre-selected excel file.
var ExcelToJSON = function() {
this.parseExcel = function( file ) {
var reader = new FileReader();
reader.onload = function(e) {
var data = e.target.result;
var workbook = XLSX.read(data, {
type: 'binary'
});
workbook.SheetNames.forEach(function(sheetName) {
var XL_row_object = XLSX.utils.sheet_to_row_object_array(workbook.Sheets[sheetName]);
var json_object = JSON.stringify(XL_row_object);
console.log(JSON.parse(json_object));
jQuery('#xlx_json').val(json_object);
})
};
reader.readAsBinaryString(file);
};
};
function handleFileSelect(evt) {
var files = evt.target.files; // FileList object
var xl2json = new ExcelToJSON();
xl2json.parseExcel(files[0]);
}
document.getElementById('upload').addEventListener('change', handleFileSelect, false);
Here instead of browsing a file, i want to open the file '../img/file.xlsx' and convert it into an object. What is the best way to do it?

Did you try using xlsx?
install using
npm install xlsx
to read file,
const reader = require('xlsx')
const file = reader.readFile('../img/file.xlsx')

How to set a FILE Name while downloading a file from FileReader?

I'm trying to download a file from a server using FileReader, when it downloads the file like download.zip, but I want to set some different file names here.
var newBlob = new Blob([blob], { type: blob.type })
var reader = new FileReader();
reader.onload = function(e){
window.location.href = reader.result ? reader.result.toString() : "";
}
reader.readAsDataURL(newBlob);

You can update the file name of what you want using the reader.fileName
var reader = new FileReader();
reader.fileName = file.name // file came from a input file element
reader.onload = function(readerEvt) {
console.log(readerEvt.target.fileName);
};

Read Simple JSON file (almost done)

I have a input and when I load it shows the file right in console.log.
But how do I get the actual json data from the file??
$('#importFlow').change(function () {
var files = event.target.files;
var file = files[0];
console.log(file);
console.log(JSON.parse(file)); //doesn't work
});

You'd need to use the FileReader API.
$('#importFlow').change(function () {
var files = event.target.files;
var file = files[0];
var reader = new FileReader();
reader.onload = function(event) {
var jsonObject = JSON.parse(event.target.result);
console.log(jsonObject); // Logs the parsed JSON
}
reader.readAsText(file);
});

You can read actual file content like this:
$('#importFlow').change(function () {
var files = event.target.files;
var reader, fileContent;
if (this.files)
{
reader = new FileReader();
reader.onload = function (e)
{
fileContent = e.target.result;
}
reader.readAsDataURL(this.files[0]);
}
});
In the above code, you can get the actual file data in the "fileContent" variable.

Filereader JS API not reading files properly

I have written the following code to read text from any csv or text file. However it sometimes reads successfully and stores in the variable and sometimes doesn't. Is there something missing in my code.
groupCsvData = [];
$('#add-group-upload').change(function() {
var file = this.files[0];
var reader = new FileReader();
reader.onload = function(e) {
var text = reader.result;
groupCsvData = [text];
};
reader.readAsText(file);
)};

Using Javascript FileReader with huge files

I have a problem using the Javascript FileRead trying to read huge files.
For example, I have a text file of 200mb and everytime I read this file the code stops working.
Its possible to read the text file, but for example ONLY the first 10 lines or stop reading after 10mb?
This is my code:
var file = form.getEl().down('input[type=file]').dom.files[0];
var reader = new FileReader();
reader.onload = (function(theFile) {
return function(e) {
data = e.target.result;
form.displayedData=data;
};
})(file);
reader.readAsText(file);
The e.target.result always has the whole data of the file.
What can I do here?
Thx

This will only read the first 10 mb:
var file = form.getEl().down('input[type=file]').dom.files[0];
var reader = new FileReader();
reader.onload = function(e) {
var data = e.target.result;
form.displayedData = data;
};
reader.readAsText(file.slice(0, 10 * 1024 * 1024));