Js check upload file size

check_file_upload.js

// This awesome jQuery plugin will check the file size and against the selected upload file and
// determine if its allowable. The size limit will have to be in bytes.
// Parameters: 
//	evt_type - the javascript event, if non is needed, set to empty string
//	limit - the size limit in bytes (default javascript size measurement)

$.fn.fileSizeCheck = function(evt_type, limit) {
	var sizeLimit = limit;

	if (evt_type == "") {
		checkSize($(this).attr('id'));
	} else {
		$(this).bind("" + evt_type + "", function() {
			checkSize($(this).attr('id'));
		});
	}

	function checkSize(id) {
		upload_id = id;
	  input = document.getElementById("" + upload_id + "");

	  if (window.FileReader && input.files[0]) {
	    file = input.files[0];

	    if (file.size > sizeLimit) {
	    	// Clear the upload input field
	    	document.getElementById(""+upload_id+"").value = '';

	    	// Generate actual size of file
	      err_msg = bytesToSize(file.size);

	      // Display warning to user
	      var warn_sg = $("#"+upload_id).next();
	      if ($(warn_sg).attr('class') != 'file_size_warn') {
	    		$("#"+upload_id).after('<span class="file_size_warn" style="color: red;">File size greater than allowed, current size: ' + err_msg + '.</span>')
	    	}
	    } else {
	    	// Remove warning if file meets size limit
	    	var warn_sg = $("#"+upload_id).next();
	    	if ($(warn_sg).attr('class') == 'file_size_warn') {
	    		$(warn_sg).remove();
	    	}
	    }
	  }
	}

	// http://stackoverflow.com/questions/15900485/correct-way-to-convert-size-in-bytes-to-kb-mb-gb-in-javascript
	function bytesToSize(bytes) {
	   var sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
	   if (bytes == 0) return '0 Byte';
	   var i = parseInt(Math.floor(Math.log(bytes) / Math.log(1024)));
	   return Math.round(bytes / Math.pow(1024, i), 2) + ' ' + sizes[i];
	};

};

/*
Example usage:
$(".a").fileSizeCheck("change",123)

or 

$(".a").fileSizeCheck("",123)

*/