How do I read contents of multiple files with FileReader

Question

1.00/5 (1 vote)

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Hi,

I'm trying to read the contents of multiple files from JavaScript. One file works fine but if I select multiple files, onload seems to be called the appropriate number of times but only the contents of the last files are displayed. Other files are displayed as blank. Any ideas would be great.

I'm guessing the file may not have been read before I try and display but I'm not sure why. Any help would be great. Thanks,

Brian

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="utf-8">
	<title>File API</title>
    <script>
	function processFiles()
	{
		
    	var filelist = document.getElementById('files').files;

    	
		for(var i=0; i<filelist.length; i++)
		{
			
			var file = filelist[i];
			var textType = /text.*/;
			

			if (file.type.match(textType)) 
			{			
				var reader = new FileReader();
				reader.>
</head>
<body>
Select a text file: 
<input type="file" multiple id="files" onchange="processFiles()" />
</body>
</html>

Posted 7-Feb-15 3:06am

BrianHamilton

Updated 7-Feb-15 5:25am

v4

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Comments

Sergey Alexandrovich Kryukov 7-Feb-15 9:53am

What's the difference, one file or more? You don't show where you "display" the file. Maybe you write the data to the same place. :-)
—SA

2 solutions

Solution 1

Try this:

XML

<!DOCTYPE html>
<html>
<head>
</head>
<body>
<input type='file' accept='text/plain' onchange='openFile(event)'><br>
<ul id='filelist'></ul>
<script>
  var openFile = function(event) {
    var input = event.target;

    var reader = new FileReader();
    reader.onload = function(){
      var text = reader.result;
      var ul = document.getElementById("filelist");
      var li = document.createElement("li");
      li.innerHTML = reader.result;
      ul.appendChild(li);
    };
    reader.readAsText(input.files[0]);
  };
</script>

</body>
</html>

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BrianHamilton · Accepted Answer · 2015-02-07T07:33:00

XML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>File API</title>
    <script>
    function processFiles()
    {
        var filelist = document.getElementById('files').files;
        for(var i=0; i<filelist.length; i++)
        {
            writefiles(filelist[i]);
        }
    }

    function writefiles(file)
    {
        var reader = new FileReader();
        reader.onload = function()
        {
            document.getElementById('output').innerText += reader.result;
        }
        reader.readAsText(file, "UTF-8");
    }
    </script>
</head>
<body>
Select a text file:
<input type="file" accept='text/plain' multiple id="files" onchange="processFiles()" />
<pre id="output"></pre>
</body>
</html>