How can I make the animations be run one by one?

Question

The HTML code:

<ul>
    <li>a</li>
    <li>b</li>
    <li>c</li>
    <li>d</li>
    <li>e</li>
</ul>

The js code:

<script type="text/javascript">
$(document).ready(function() {
    var lis = $("li");
    for (var i = 0; i < lis.length; i++) {
        $(lis[i]).animate({opacity: 0}, 1000);
    }
});
</script>

I just find that the lis will disappear together. How can I do that they will disappear one by one?

Answer 1

Sorry for joining the party late.

The existing answers have issues when a timer blocks and rely on the accuracy of timers, moreover they require an actual delay.

jQuery actually provides a generic way to perform animations sequentially with promises:

$(document).ready(function() {
    var lis = $("li");
    var queue = $.Deferred().resolve(); // create an empty queue
    lis.get().forEach(function(li){
        queue = queue.then(function(){
           return $(li).animate({opacity: 0}, 1000).promise();
        })
    });
});

Fiddle

Note that this will work even if you assign them different animation durations or different animations, the result in queue will contain a hook on when the last animation finished. This also supports aggregations (waiting for all promises to finish in parallel) and more.