onclick in button tag in html code example

Example 1: onclick a tag

<a href='http://www.google.com' onclick='return check()'>check</a>

<script type='text/javascript'>
function check() {
    return false;
}
</script>

Example 2: javascript onclick

var myElem = document.getElementByID('ElemID');
myElem.onclick = function() {
	//do stuff
}