Check if Function Exists before Calling? (ok)

https://stackoverflow.com/questions/13657204/check-if-function-exists-before-calling

if ( $.isFunction($.fn.lettering) ) {
    $(".cs-text-cut").lettering('words');
}

<script>
if ( typeof function_name == 'function' ) { 
        //function_name is a function
}
else
{
 //do not exist
}
</script>