get the data of uploaded file in javascript

Question

I want to upload a csv file and process the data inside that file. What is the best method to do so? I prefer not to use php script. I did the following steps. But this method only returns the file name instead of file path.So i didnt get the desired output.

<form id='importPfForm'>
<input type='file' name='datafile' size='20'>
<input type='button' value='IMPORT' onclick='importPortfolioFunction()'/>
</form>

function importPortfolioFunction( arg ) {
    var f = document.getElementById( 'importPfForm' );
    var fileName= f.datafile.value;   
}

So how can i get the data inside that file?

Duplicate of http://stackoverflow.com/questions/5028931/is-it-possible-to-read-a-file-using-javascript and about a dozen other questions. Please use the search box next time. — Ray Nicholus, May 12 '13 at 14:03
Not quite. That question is about AJAX. This seems to be 'upload a file so the browser can then manipulate it'. It doesn't mention uploading it to a server. — Andrew Murphy, Sep 15 '16 at 16:16

score 73 · Answer 1 · edited Oct 29 '21 at 10:38

The example below is based on the html5rocks solution. It uses the browser's FileReader() function. Newer browsers only.

See http://www.html5rocks.com/en/tutorials/file/dndfiles/#toc-reading-files

In this example, the user selects an HTML file. It is displayed in the <textarea>.

<form enctype="multipart/form-data">
<input id="upload" type=file   accept="text/html" name="files[]" size=30>
</form>

<textarea class="form-control" rows=35 cols=120 id="ms_word_filtered_html"></textarea>

<script>
function handleFileSelect(evt) {
    let files = evt.target.files; // FileList object

    // use the 1st file from the list
    let f = files[0];
    
    let reader = new FileReader();

    // Closure to capture the file information.
    reader.onload = (function(theFile) {
        return function(e) {
          
          jQuery( '#ms_word_filtered_html' ).val( e.target.result );
        };
      })(f);

      // Read in the image file as a data URL.
      reader.readAsText(f);
  }

  document.getElementById('upload').addEventListener('change', handleFileSelect, false);
</script>

Promise was made to remove JQuery two years ago but it's still in the code: `jQuery( '#ms_word_filtered_html' ` — WinEunuuchs2Unix, May 02 '22 at 11:45

score 38 · Accepted Answer · answered May 12 '13 at 08:36

38

you can use the new HTML 5 file api to read file contents

https://developer.mozilla.org/en-US/docs/Using_files_from_web_applications

but this won't work on every browser so you probably need a server side fallback.

answered May 12 '13 at 08:36

Woody

7,578
2
21
25

score 33 · Answer 3 · edited Jun 22 '21 at 08:37

The example below shows the basic usage of the FileReader to read the contents of an uploaded file. Here is a working Plunker of this example.

function init() {
  document.getElementById('fileInput').addEventListener('change', handleFileSelect, false);
}

function handleFileSelect(event) {
  const reader = new FileReader()
  reader.onload = handleFileLoad;
  reader.readAsText(event.target.files[0])
}

function handleFileLoad(event) {
  console.log(event);
  document.getElementById('fileContent').textContent = event.target.result;
}

<!DOCTYPE html>
<html>

<head>
  <script src="script.js"></script>
</head>

<body onload="init()">
  <input id="fileInput" type="file" name="file" />
  <pre id="fileContent"></pre>
</body>

</html>

score 13 · Answer 4 · answered Jul 30 '21 at 22:35

There exist some new tools on the blob itself that you can use to read the files content as a promise that makes you not have to use the legacy FileReader

// What you need to listen for on the file input
function fileInputChange (evt) {
  for (let file of evt.target.files) {
    read(file)
  }
}

async function read(file) {
  // Read the file as text
  console.log(await file.text())
  // Read the file as ArrayBuffer to handle binary data
  console.log(new Uint8Array(await file.arrayBuffer()))
  // Abuse response to read json data
  console.log(await new Response(file).json())
  // Read large data chunk by chunk
  console.log(file.stream())
}

read(new File(['{"data": "abc"}'], 'sample.json'))

Excellent answer, thanks! – Steve Bauman Nov 23 '21 at 00:03 — Steve Bauman, Nov 23 '21 at 00:03
The only answer that worked! Thanks! – Matteo Aug 17 '23 at 05:38 — Matteo, Aug 17 '23 at 05:38

score 2 · Answer 5 · answered Jul 30 '21 at 10:19

Try This

document.getElementById('myfile').addEventListener('change', function() {


          var GetFile = new FileReader();
        
           GetFile .onload=function(){
                
                // DO Somthing
          document.getElementById('output').value= GetFile.result;
        
        
        }
            
            GetFile.readAsText(this.files[0]);
        })

    <input type="file"  id="myfile">


    <textarea id="output"  rows="4" cols="50"></textarea>

There is no need to bump a old Q with a similar answer (like the one provided by others here). — Endless, Jul 30 '21 at 22:24

score -1 · Answer 6 · answered Oct 11 '18 at 09:25

-1

FileReaderJS can read the files for you. You get the file content inside onLoad(e) event handler as e.target.result.

answered Oct 11 '18 at 09:25

Slawa

1,141
15
21

get the data of uploaded file in javascript

6 Answers6

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