jQuery animate lineHeight - relative property gives weird result

问题

I am trying to increase the font size within a page and therefore also adjust the line height accordingly. Now I saw that I can use relative values for the font-size, but somehow this doesn't work for the line-height!?

$('elem').on('click', function () {
  box.animate({
    'lineHeight':  '+=5',
    'fontSize': '+=5'
  });
});

Is there another way then:

var lh = parseFloat( box.css('line-height'), 10);

$('elem').on('click', function () {
  lh += 5;
  box.animate({
    'lineHeight':  lh + 'px',
    'fontSize': '+=5'
  });
});

?

thanks

来源：https://stackoverflow.com/questions/9840983/jquery-animate-lineheight-relative-property-gives-weird-result