a function that takes a character (i.e. a string of length 1) and returns true if it is a vowel, false otherwise in javascript : below is my code for finding out if a character is a vowel or not. But when I run it, it doesn't print out true or false. Can someone please help me to see what I am doing wrong? 
BTW, I am new to JS.
TIA.

    >    <!DOCTYPE html>
       <html>
       <head>
    	<meta charset="utf-8">
    	<title>finding the vowels in a string</title>
    	</head>
    	<body>
    	
    	<form>
    	<input type = "text" name = 't1'>
    	<input type = 'submit' value = "SUBMIT" onClick = 'return vowel(this.form.t1.v'>
    	<div id="p"></div>
    	</form>
       <script>
    	var vowel = function(str)	{
    		var matches = str.match(/[aeiou]/gi);
    		var count = matches ? matches.length: 0;
    		
    		document.getElementByID('p').innerHTML = "'"+str+"contains"+count+"vowel(s)";
    		
    		return false;
    		};
    	vowel(str);
    </script>
    
    </body>
    </html> 
    				