FileReader onload with result and parameter

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I can't manage to get both the result of the filereader and some parameters in a onload function. This is my code:

HTML of control:

<input type="file" id="files_input" multiple/>

Javascript function:

function openFiles(evt){
    var files = evt.target.files;
    for (var i = 0; i < files.length; i++) {
      var file=files[i];
      reader = new FileReader();
      reader.onload = function(){
          var data = $.csv.toArrays(this.result,{separator:'\t'});
      };
      reader.readAsText(file);
    }
  }

Add event:

 files_input.addEventListener("change", openFiles, false);

I use the filereader.result, in the onload function. If I use a parameter, like file, for this function, I can't not access to the result anymore. For example I'd like to use file.name in the onload function. How to resolve this issue ?

Pass a parameter to FileReader onload event, result); }; })(currFile); reader.readAsText(currFile);. Here, you're creating a new fileName variable each time  FileReader onload with result and parameter Tag: javascript , filereader I can't manage to get both the result of the filereader and some parameters in a onload function.

You should use closure at 'onload' handler. Example: http://jsfiddle.net/2bjt7Lon/

reader.onload = (function (file) { // here we save variable 'file' in closure
     return function (e) { // return handler function for 'onload' event
         var data = this.result; // do some thing with data
     }
})(file);

FileReader.onload, The FileReader.onload property contains an event handler executed when file's text will be printed here console.log(e.target.result) }; reader. The FileReader() constructor creates a new FileReader. For details about how to use FileReader, see Using files from web applications. Syntax var reader = new FileReader(); Parameters. None. Example. The following code snippet shows creation of a FileReader object using the FileReader() constructor and subsequent usage of the object:

Event handling is asynchronous and thus they pick up the latest value of all the enclosed local variables(i.e. closure). To bind a particular local variable to the event, you need to follow the code suggested by users above or you can look at this working example:-

http://jsfiddle.net/sahilbatla/hjk3u2ee/

function openFiles(evt){
  var files = evt.target.files;
  for (var i = 0; i < files.length; i++) {
    var file=files[i];
    reader = new FileReader();
    reader.onload = (function(file){
      return function() {
        console.log(file)
      }
    })(file);
    reader.readAsText(file);
  }
}

#Using jQuery document ready
$(function() {
  files_input.addEventListener("change", openFiles, false);
});

FileReader.onLoad/onLoadEnd event argument has no target.result , Trying to retrieve the result of a read file/blob via the event passed into the reader's onload/onloadend method results in a type error (Property  j'utilise filereader.result, dans le onload fonction. Si j'utilise un paramètre, comme fichier, pour cette fonction, Je ne peux plus accéder au résultat. Par exemple je voudrais utiliser file.name dans la fonction onload. Comment faire pour résoudre ce problème ?

For Typescript;

for (var i = 0; i < files.length; i++) {
  var file = files[i];

  var reader = new FileReader();

  reader.onload = ((file: any) => {
    return (e: Event) => {
      //use "e" or "file"
    }
  })(file);

  reader.readAsText(file);
}

Reading Files with FileReader, The FileReader API is really handy if you need to read a file using JavaScript. There's a whole Pass in a File or Blob object as the file parameter. var reader = new FileReader(); reader.onload = function(e) { var text = reader.result; } reader​. This ensures that that operation will not run until the reader's onload callback fires, when e.target.result will be filled. Programming with callbacks is a bit difficult to get right at first, but it is absolutely necessary for implementing advanced functionality.

As the variable file is within the scope, you may use the file variable without passing it to function.

function openFiles(evt){
    var files = evt.target.files;
    for (var i = 0; i < files.length; i++) {
          var file=files[i];    
          reader = new FileReader();
          reader.onload = function(){
              alert(file.name);
              alert(this.result);
          };
      reader.readAsText(file);
    }
  }

files_input.addEventListener("change", openFiles, false);
<input type="file" id="files_input" multiple/>

FileReader JavaScript API, The result is only available after the load event fires. Example: <input type='file' accept='image/*' onchange='openFile(event)'><  FileReader.result return null. I'm trying to setup a page that lets you upload a txt file (namely a log file that another program generates), and then manipulate the text further. So far I just want to console.log the text, but later on I'm planning to separate lines and get some specifics out of it to run my program. There's the snippet.

javascript - Pass a parameter to FileReader onload event -, currfile.name; var reader = new filereader(); reader.onload = (function(thefile){ return function(e){ var csvarr = csv.csvtoarray( e.target.result,  FileReader.readAsDataURL() is asynchronous - the download happens in the background while the rest of the code keeps executing. So the reason console.log(my_pdf_file_as_base64); prints an empty string is that the line my_pdf_file_as_base64 = e.target.result hasn't been executed yet: the call to getBase64() finishes almost immediately, and the subsequent statement is executed; only later (when

Working with files in JavaScript, Part 2: FileReader, var reader = new FileReader(); reader.onload = function(event) { var and it's recommended to use that instead of referencing the reader variable directly. The result property contains the file contents on success and error  The FileReader interface's readAsArrayBuffer () method is used to start reading the contents of a specified Blob or File. When the read operation is finished, the readyState becomes DONE, and the loadend is triggered. At that time, the result attribute contains an ArrayBuffer representing the file's data.

javascript filereader onload - Search, Results from the Web. javascript - FileReader onload with result and parameter stackoverflow.com. If browser has FileReader, I think it supports forEach and  I am struggling trying to re-work the idea/code found here (basic premise being working out a file type by simply looking at the first few bytes of data). Ive got the bare bones of doing what i wa

Comments
  • does it work with one file? Try creating different readers, add "var reader = new FileReader();"
  • Use a simple rule: Declare all your local variables at the beginning of the closure. Don't declare them inside for, in, and other similar statements, because these statements do not create closures and consequently the declared variables are not local to the statement. This will help you determine when you need to create additional closures.
  • If browser has FileReader, I think it supports forEach and bind :) I think better use bind for adding file to onload callback
  • @Pinal that is a good suggestion. I won't update my answer to include these, since I wanted to keep my answer as close to the code supplied by the OP and only change what is necessary (introduce the closure), but it is good to be aware of these features.
  • In a similar vain, in production code I'd be tempted to move the FileReader code into it's own named function called from the loop. Closures would behave as expected and it helps break down the code. That said the example as given is more appropriate for demonstrating the technical solution.
  • if i could i would upvote this answer 1000 times. Thank you !
  • Thanks mate! Helped me a lot!
  • This isn't quite right. You should assign a function to reader.onload. The IIFE you are invoking doesn't return anything, so no code will run once the reader has fired its load event.
  • I don't clearly understand why returning a function is important, when the piece of code will run only on the onload event and has file binded to it
  • Currently, your function (function(file){console.log(file)})(file); is run once for each iteration of your for loop. It doesn't return anything, so reader.onload = undefined for each interation of the loop. Therefore, while your console.log does print the correct file name, nothing will run when reader has fired it's load event.
  • Thanks for highlighting that, its my bad, I should fix this
  • Thanks yeah got it :) But this seems to be working when I tested by displaying each file name and content. Run Code Snippet above. I guess I am missing something will see.
  • The above code works in this case because the onload event occurs as part of the iteration (reader.readAsText). Whereas in stackoverflow.com/questions/1451009 onclick event occurs after the iteration is completed
  • Whilst this may appear to work, when you run the above snippet and select multiple files the last file in the list is displayed multiple times. So this does not work as expected.