Reading a file using JavaScript

FileReader object in JavaScript can read the content of a file using File or Blob objects.

Let us see an example, as code can explain things much better than theory...

For example.
<html>
<head>
<title>Reading a file in JavaScript</title>
</head>
<body>

	<input type="file" id="files" multiple />
	<div id="fileContent"></div>
</body>
<script>

function fileSelected(evt) {
    var files = evt.target.files;

	var fr = new FileReader();
	fr.onload = function(event)
	{
		document.getElementById('fileContent').innerHTML = event.target.result;
	}
	
    for (var i = 0, f; f = files[i]; i++) {
      
	  //Gives name of file : f.name
	  //Gives type of file : f.type e.g. text/plain or image/png etc
	  //Gives size of file : f.size (in bytes)
	  //Gives last modified date : f.lastModifiedDate
	  
	  var fileCopy = f.slice(0, f.size); //i.e. read entire file
	  
	  //If we wish to read file from beginning to half lenght, then
	  //var fileCopy = f.slice(0, f.size / 2); //i.e. read entire file
	  
	  fr.readAsText(fileCopy); //on successful read, fr.onload function will be called and that will populate the result in fileContent container
    }
    //document.getElementById('fileContent').innerHTML = str;
  }
  
  //attach change event of file control
  document.getElementById('files').addEventListener('change', fileSelected, false);
</script>
</html>
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