Check out example codes for "onclick a tag". It will help you in understanding the concepts better.

Code Example 1

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

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

Code Example 2

<a href="javascript:show_more_menu();">More >>></a>

Learn ReactJs, React Native from akashmittal.com