File upload Preview // single file

gistfile1.js

fileUploadPreview = function () {

  var self = this,

	uploader = document.getElementById("files"),
	output = document.getElementById('preview_image'),


	initialise = function() {
		uploader.addEventListener('change', handleFileSelect, false);
	},

	handleFileSelect =  function(e) {
		var files = e.target.files,
			f= files[0]; // FileList object

		var reader = new FileReader();

		reader.onload = (function(theFile) {

			return function(e) {
				var span = document.createElement('span');
				span.innerHTML = ['<img class="thumb" src="', e.target.result, '" title="', escape(theFile.name), '"/>'].join('');
				output.innerHTML = "";
				output.insertBefore(span, null);
			};

		})(f);

		reader.readAsDataURL(f);
	};


	if (window.File && window.FileReader && window.FileList && window.Blob) {
		initialise();
	}



  return this;
};