I implemented a solution in your function to stop execution early if the end tab is reached:
if (to === 'right' && current === (total - 1)) {
return;
} else if(to === 'left' && current === 0) {
return;
}
To see it in action, check out this working example: https://codepen.io/anon/pen/RZeNWq?editors=0001
On another note, I recommend considering the broader context when selecting DOM elements. For instance, in your code snippet:
var current = $('li.current').index();
An li element with the class current is quite general - if there happens to be an unrelated li tag with the same class elsewhere on your page, it could cause issues. What if you had a navigation bar where menu items also used the class current? Or if your page featured two sets of tabs, this code wouldn't accommodate that.
A more resilient approach would be something like:
var current = $('.tab-link.current').index();