javascript - 如何从 Promise 返回字符串

Question

我正在使用 vue 开发一个网站，我必须使用 axios 从服务器获取图像并将它们作为 div 的背景图像。情况是我有网址，但并非所有网址都是正确的。因此，我尝试创建一个函数来发出 http 请求，并在请求成功时返回 url。

我想到了这样的事情:

模板:

<div class="element" :style="bgImg(url)"/>

脚本:

methods: {
  bgImg(url) {
    axios.get(url)
      .then(response => {
        return `background-image: url(${response.config.url})`;
      })
      .cath(e) {
        throw new Error(e);
      }
  }
}

我本来希望得到该函数返回的 url，但什么也没发生。

Answer 1

您可以使用 custom vue directive对于该工作:

Vue.directive('validate-bgimg', function (el, binding) {  
  el.style.backgroundImage = null  // reset 
  var url = binding.value
  if (!url) {
    return
  }
  axios.get(`https://cors-anywhere.herokuapp.com/${url}`)  // get around CORS limitations. Idealy you should call your own api to validate image urls
  .then(response => {
    if (response.status != 200) {
      console.warn("Invalide image url", url, response)
    } else {
      el.style.backgroundImage = `url(${url})`
    }
  })
  .catch(e => {
    console.error("Could not validate image", url, e)
  })
})


new Vue({
  el: "#app",
  data: {
    imgUrl: undefined
  }
})

#app {
  background: lightgray;
  border-radius: 4px;
  padding: 20px;
  margin: 20px;
  transition: all 0.2s;
}

.element {
  margin: 8px 0;
  width: 200px;
  height: 200px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/axios/0.18.0/axios.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<div id="app">
  <b>test case:</b>
  <button @click="imgUrl='https://dummyimage.com/200x200/000/fff.gif&text=test+1'">1</button>
  <button @click="imgUrl='https://dummyimage.com/200x200/000/fff.gif&text=test+2'">2</button>
  <button @click="imgUrl='https://dummyimage.com/200x200/000/fff.gif&text=test+3'">3</button>
  <button @click="imgUrl='https://httpbin.org/status/404'">HTTP 404</button>
  <button @click="imgUrl='https://httpbin.org/status/503'">HTTP 503</button>
  <button @click="imgUrl='https://invalid.tld'">cannot resolve domain name</button>
  
  <div class="element" v-validate-bgimg="imgUrl"/>
</div>