How to increase/decrease current margin at a number by jquery?

Question

Given an element with unknown margin-left, how to increase its margin-left at a number say 100px?

For example:

assuming the original margin-left is 100px

Answer 1

$('#element-id').css('margin-left', function (index, curValue) {
    return parseInt(curValue, 10) + 100 + 'px';
});

curValue will include 'px' at the end, so you'll end up with NaN or 100px100px as your result without using parseInt first.