有没有更好的方法来实现没有Javascript的CSS动画？

Question

Just experimenting with a loading bar. The primary issue is, once each bar is done with its iteration, it needs to start again on top of the last bar. I did this via some hacky JS but maybe there's a more clever way to do it using pure CSS?

HTML

<div class="loading-bar">
    <div class="bar"><div class="bar-inner"></div></div>
    <div class="bar"><div class="bar-inner"></div></div>
</div>

SCSS

.loading-bar {
    clear: both;
    height: 12px;
    width: 100%;

    position: relative;

    .bar {
        margin: 0 auto;
        height: 12px;
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        text-align: center;
        z-index: 0;

        .bar-inner {
            margin: 0 auto;
            width: 0;
            height: 12px;            
            -webkit-animation-name: loadbars;
            -webkit-animation-duration: 1s;
            -webkit-animation-iteration-count: infinite;
            -webkit-animation-timing-function: ease-in-out;
        }

        &:nth-child(1) .bar-inner {
            background: gray;            
        }
        &:nth-child(2) .bar-inner {
            background: blue;
            -webkit-animation-delay: 0.5s;
        }             
    }
}

@-webkit-keyframes loadbars {
    0% { width: 0; }

    50% { width: 100%; }

    100% { width: 100%; }
}

JS

var bars = $(".bar-inner");
var zindex = 1;
var listener = function () {
    zindex++;
    $(this).parent().css("z-index", zindex);    
};

bars.on("webkitAnimationIteration", listener);

Demo: http://jsfiddle.net/18uqrtxo/

Updated

I've updated the demo to show pure CSS with 4 bars, just for fun.

http://jsfiddle.net/18uqrtxo/2/

Answer 1

Animate the z-index .

Demo

Apply the z-index to the bars, not their containers. This will allow the bar to be on top when it's getting wider, and underneath when it's at full width.