Question

var str = $('.rating').html();
$.trim(str);
$('.rating').prepend.attr('class', 'rating-' + str.replace(/\s/g, ""));

<div class="rating">1</div>
<div class="rating">2</div>
<div class="rating">3</div>

Change to this:
<div class="rating-1">1</div>
<div class="rating-2">2</div>
<div class="rating-3">3</div>

How does .prepend work with .attr ? Seems I can’t find any information about append and attr.

All I want to do is select an class and replace them with class-1, class-2, class-3 etc.

Answer 1

prepend and append operate on DOM elements, not strings. Use removeClass and addClass to accomplish what you are trying to:

$('.rating').removeClass("rating").addClass(function () {
    return "rating-" + $(this).html();
});