Javascript read line by line text file

Question

Javascript:

<script src="../plugin/jquery-3.1.0.min.js"></script>
<script>
    $(document).ready(function(){
       $('#test').click(function(){
           var txtFile = '../fileupload/mail.txt';
           var file = new File(txtFile);
           file.open("r");
           while (!file.eof) {
               alert(file.readln());
           }
           file.close();
       });
    });
</script>

HTML:

<button type="submit" class="btn btn-default" id="test">Check</button>

When i click check button, Javascript will read file line by line. But it does not run :(. Please help me fix it

Do you know if the click event being fired? i.e: have you put a `console.log` in the click function — Benji Lees, May 03 '17 at 08:27
See https://developer.mozilla.org/en-US/docs/Web/API/File/File — Benji Lees, May 03 '17 at 08:29

score 4 · Answer 1 · edited May 23 '17 at 11:33

You cannot read files that way from browser-hosted JavaScript. The File constructor doesn't accept just one argument, and File objects don't have open, readln, or close methods nor an eof property. Whatever reference you're looking at, it's not for the browser-based File object.

If you're running this from a proper web page, you can read resources from your own server via ajax (XMLHttpRequest or fetch).

If you're trying to read a local file, you'll have to have the user identify the file (you can't do it for them) via an input type="file", and then use the File API to read the contents of the file. This answer has an example of doing that (both in text and binary).

score 2 · Answer 2 · answered May 03 '17 at 08:52

If you are looking to create and then download a file i would suggest that you take a look at file saver

var blob = new Blob(["r"], {type: "text/plain;charset=utf-8"});
saveAs(blob, "mail.txt");

else if you are looking to upload a file I would add a input type="file" id="file-test" and then use FileReader.

 $('#file-test').change(function(e) {
   var doc = event.target.files.document;
   var reader = new FileReader();
   reader.onload = function(event) {
     // Then you can do something with the result
     console.log(event.target.result)
   };

   reader.readAsText(doc);
 }

Javascript read line by line text file

2 Answers2