el-button加上涟漪动画效果

要给`el-button`加上涟漪动画效果，需要使用`waves`指令来实现。具体步骤如下：

1. 首先，需要在`<template>`标签中引入`waves.css`文件，该文件用于控制涟漪动画效果的样式，代码如下：

<template>
  <div>
    <link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/waves.css">
    <el-button v-waves>点击我</el-button>
  </div>
</template>

2. 然后，在`<script>`标签中注册`waves`指令，代码如下：

export default {
  directives: {
    waves: {
      bind(el, binding) {
        el.addEventListener('mousedown', e => {
          const customOpts = Object.assign({}, binding.value)
          const opts = Object.assign({
            ele: el, // 波纹作用元素
            type: 'hit', // hit 点击位置扩散 center中心点扩展
            color: 'rgba(0, 0, 0, 0.15)' // 波纹颜色
          }, customOpts)
          const target = opts.ele
          if (target) {
            target.style.position = 'relative'
            target.style.overflow = 'hidden'
            const rect = target.getBoundingClientRect()
            let ripple = target.querySelector('.waves-ripple')
            if (!ripple) {
              ripple = document.createElement('span')
              ripple.className = 'waves-ripple'
              ripple.style.height = ripple.style.width = Math.max(rect.width, rect.height) + 'px'
              target.appendChild(ripple)
            } else {
              ripple.className = 'waves-ripple'
            }
            switch (opts.type) {
              case 'center':
                ripple.style.top = (rect.height / 2 - ripple.offsetHeight / 2) + 'px'
                ripple.style.left = (rect.width / 2 - ripple.offsetWidth / 2) + 'px'
                break
              default:
                ripple.style.top = (e.pageY - rect.top - ripple.offsetHeight / 2 - document.documentElement.scrollTop) + 'px'
                ripple.style.left = (e.pageX - rect.left - ripple.offsetWidth / 2 - document.documentElement.scrollLeft) + 'px'
            }
            ripple.style.backgroundColor = opts.color
            ripple.className = 'waves-ripple z-active'
            return false
          }
        }, false)
      }
    }
  }
}

3. 最后，在`<el-button>`标签中添加`v-waves`指令即可，代码如下：

<template>
  <div>
    <link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/waves.css">
    <el-button v-waves>点击我</el-button>
  </div>
</template>

<script>
export default {
  directives: {
    waves: {
      bind(el, binding) {
        el.addEventListener('mousedown', e => {
          const customOpts = Object.assign({}, binding.value)
          const opts = Object.assign({
            ele: el, // 波纹作用元素
            type: 'hit', // hit 点击位置扩散 center中心点扩展
            color: 'rgba(0, 0, 0, 0.15)' // 波纹颜色
          }, customOpts)
          const target = opts.ele
          if (target) {
            target.style.position = 'relative'
            target.style.overflow = 'hidden'
            const rect = target.getBoundingClientRect()
            let ripple = target.querySelector('.waves-ripple')
            if (!ripple) {
              ripple = document.createElement('span')
              ripple.className = 'waves-ripple'
              ripple.style.height = ripple.style.width = Math.max(rect.width, rect.height) + 'px'
              target.appendChild(ripple)
            } else {
              ripple.className = 'waves-ripple'
            }
            switch (opts.type) {
              case 'center':
                ripple.style.top = (rect.height / 2 - ripple.offsetHeight / 2) + 'px'
                ripple.style.left = (rect.width / 2 - ripple.offsetWidth / 2) + 'px'
                break
              default:
                ripple.style.top = (e.pageY - rect.top - ripple.offsetHeight / 2 - document.documentElement.scrollTop) + 'px'
                ripple.style.left = (e.pageX - rect.left - ripple.offsetWidth / 2 - document.documentElement.scrollLeft) + 'px'
            }
            ripple.style.backgroundColor = opts.color
            ripple.className = 'waves-ripple z-active'
            return false
          }
        }, false)
      }
    }
  }
}
</script>

这样就可以给`el-button`添加涟漪动画效果了。