javascript - Why are CSS keyframe animations broken in Vue components with scoped styling?

Question

I'm trying to implement a CSS typing indicator in Vue. Without Vue, it looks like this:

.typing-indicator {
  background-color: #E6E7ED;
  width: auto;
  border-radius: 50px;
  padding: 20px;
  display: table;
  margin: 0 auto;
  position: relative;
  -webkit-animation: 2s bulge infinite ease-out;
          animation: 2s bulge infinite ease-out;
}
.typing-indicator:before, .typing-indicator:after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: -2px;
  height: 20px;
  width: 20px;
  border-radius: 50%;
  background-color: #E6E7ED;
}
.typing-indicator:after {
  height: 10px;
  width: 10px;
  left: -10px;
  bottom: -10px;
}
.typing-indicator span {
  height: 15px;
  width: 15px;
  float: left;
  margin: 0 1px;
  background-color: #9E9EA1;
  display: block;
  border-radius: 50%;
  opacity: 0.4;
}
.typing-indicator span:nth-of-type(1) {
  -webkit-animation: 1s blink infinite 0.3333s;
          animation: 1s blink infinite 0.3333s;
}
.typing-indicator span:nth-of-type(2) {
  -webkit-animation: 1s blink infinite 0.6666s;
          animation: 1s blink infinite 0.6666s;
}
.typing-indicator span:nth-of-type(3) {
  -webkit-animation: 1s blink infinite 0.9999s;
          animation: 1s blink infinite 0.9999s;
}

@-webkit-keyframes blink {
  50% {
    opacity: 1;
  }
}

@keyframes blink {
  50% {
    opacity: 1;
  }
}
@-webkit-keyframes bulge {
  50% {
    -webkit-transform: scale(1.05);
            transform: scale(1.05);
  }
}
@keyframes bulge {
  50% {
    -webkit-transform: scale(1.05);
            transform: scale(1.05);
  }
}
html {
  display: table;
  height: 100%;
  width: 100%;
}

body {
  display: table-cell;
  vertical-align: middle;
}

<div class="typing-indicator">
  <span></span>
  <span></span>
  <span></span>
</div>

Answer 1

Problem

The problem is down to how the Webpack loader for Vue (vue-loader), incorrectly, parses animation names when adding IDs to scoped selectors and other identifiers. This is important because vue-loader's CSS scoping uses unique attributes added to elements to replicate the behaviour of CSS scoping. While your keyframe names get IDs appended, references to keyframes in animation rules in scoped styles do not.

Your CSS:

@-webkit-keyframes blink {
  50% {
    opacity: 1;
  }

}

@keyframes blink {
  50% {
    opacity: 1;
  }
}
@-webkit-keyframes bulge {
  50% {
    -webkit-transform: scale(1.05);
            transform: scale(1.05);
  }
}
@keyframes bulge {
  50% {
    -webkit-transform: scale(1.05);
            transform: scale(1.05);
  }
}

.typing-indicator {
  ...
  -webkit-animation: 2s bulge infinite ease-out;
          animation: 2s bulge infinite ease-out;
}

.typing-indicator span:nth-of-type(1) {
  -webkit-animation: 1s blink infinite 0.3333s;
          animation: 1s blink infinite 0.3333s;
}
.typing-indicator span:nth-of-type(2) {
  -webkit-animation: 1s blink infinite 0.6666s;
          animation: 1s blink infinite 0.6666s;
}
.typing-indicator span:nth-of-type(3) {
  -webkit-animation: 1s blink infinite 0.9999s;
          animation: 1s blink infinite 0.9999s;
}

Should get transformed to:

@-webkit-keyframes blink-data-v-xxxxxxxx {
  50% {
    opacity: 1;
  }
}

@keyframes blink-data-v-xxxxxxxx {
  50% {
    opacity: 1;
  }
}
@-webkit-keyframes bulge-data-v-xxxxxxxx {
  50% {
    -webkit-transform: scale(1.05);
            transform: scale(1.05);
  }
}
@keyframes bulge-data-v-xxxxxxxx {
  50% {
    -webkit-transform: scale(1.05);
            transform: scale(1.05);
  }
}

.typing-indicator {
  ...
  -webkit-animation: 2s bulge-data-v-xxxxxxxx infinite ease-out;
          animation: 2s bulge-data-v-xxxxxxxx infinite ease-out;
}

.typing-indicator span:nth-of-type(1) {
  -webkit-animation: 1s blink-data-v-xxxxxxxx infinite 0.3333s;
          animation: 1s blink-data-v-xxxxxxxx infinite 0.3333s;
}
.typing-indicator span:nth-of-type(2) {
  -webkit-animation: 1s blink-data-v-xxxxxxxx infinite 0.6666s;
          animation: 1s blink-data-v-xxxxxxxx infinite 0.6666s;
}
.typing-indicator span:nth-of-type(3) {
  -webkit-animation: 1s blink-data-v-xxxxxxxx infinite 0.9999s;
          animation: 1s blink-data-v-xxxxxxxx infinite 0.9999s;
}

However it only get's transformed to:

@-webkit-keyframes blink-data-v-xxxxxxxx {
  50% {
    opacity: 1;
  }
}

@keyframes blink-data-v-xxxxxxxx {
  50% {
    opacity: 1;
  }
}
@-webkit-keyframes bulge-data-v-xxxxxxxx {
  50% {
    -webkit-transform: scale(1.05);
            transform: scale(1.05);
  }
}
@keyframes bulge-data-v-xxxxxxxx {
  50% {
    -webkit-transform: scale(1.05);
            transform: scale(1.05);
  }
}

.typing-indicator {
  ...
  -webkit-animation: 2s bulge infinite ease-out;
          animation: 2s bulge infinite ease-out;
}

.typing-indicator span:nth-of-type(1) {
  -webkit-animation: 1s blink infinite 0.3333s;
          animation: 1s blink infinite 0.3333s;
}
.typing-indicator span:nth-of-type(2) {
  -webkit-animation: 1s blink infinite 0.6666s;
          animation: 1s blink infinite 0.6666s;
}
.typing-indicator span:nth-of-type(3) {
  -webkit-animation: 1s blink infinite 0.9999s;
          animation: 1s blink infinite 0.9999s;
}

Something to note: in the actual transformation, references to keyframe names in animation rules are missing the -data-v-xxxxxxxx at the end. This is the bug.

Currently (as of 47c3317) the animation name in shorthand animation rule declarations is identified by getting the first value out of splitting the animation rule by any whitespace character^[1]. However the formal definition for the animation property states the animation name could appear anywhere within the rule definition.

<single-animation> = <time> || <single-timing-function> || <time> || <single-animation-iteration-count> || <single-animation-direction> || <single-animation-fill-mode> || <single-animation-play-state> || [ none | <keyframes-name> ]

– animation formal syntax^[2]

Therefore, while your animation declarations are valid, vue-loader is not able to parse it.

Workaround

The current workaround for this is to move your animation names to the beginning of animation rule declarations. Your keyframe declarations do not need changing, they remain inside the scoped stylesheet. Your animation declarations should now look like this:

.typing-indicator {
  ...
  -webkit-animation: bulge 2s infinite ease-out;
          animation: bulge 2s infinite ease-out;
}
.typing-indicator span:nth-of-type(1) {
  -webkit-animation: blink 1s infinite 0.3333s;
          animation: blink 1s infinite 0.3333s;
}
.typing-indicator span:nth-of-type(2) {
  -webkit-animation: blink 1s infinite 0.6666s;
          animation: blink 1s infinite 0.6666s;
}
.typing-indicator span:nth-of-type(3) {
  -webkit-animation: blink 1s infinite 0.9999s;
          animation: blink 1s infinite 0.9999s;
}

References

• [1] vue-loader/lib/style-compiler/plugins/scope-id.js#L67 @ 47c3317
• [2] Definition for animation in the Editor's Draft of W3C specification CSS Animations Level 1