What are the decodeURI() and encodeURI()

<script>
	var uri="my test.asp?name=ståle&car=saab";

	document.write(encodeURI(uri)+ "<br>");

	document.write(decodeURI(uri));
</script>

//output will be
my%20test.asp?name=st%C3%A5le&car=saab
my test.asp?name=ståle&car=saab