Question

$('.container').animate({ 'height': el.height()  }, { duration: 300});

So el‘s height can be smaller or greater than .container‘s height.

How can I make it so the effect duration lasts longer when the difference between the current height and the one to which I’m animating is larger?

Answer 1

var newHeight = el.height(),
    oldHeight = $('.container').height();
$('.container').animate({height: newHeight}, Math.abs(newHeight-oldHeight)*5);

Change the magic constant 5 to anything that seems reasonable. You didn’t provide criteria for computing the duration; you might bound it with Math.min(/*above expression*/, maxDuration), or maybe it shouldn’t be linear but logarithmic. You can customize it quite easily. Although that’s a good place to start.