title: Vue.js - Element UI - Use upload component without POST request triggering
body: <p>I'm using the upload component of Element UI. It unfortunately triggers a POST request as soon as a file is uploaded. What I'm aiming for is to push the files to an empty array which would be posted after with button.</p>
  
  <p><strong>HTML</strong></p>
  
  <pre><code>// Element UI documentation says http-request overrides xhr behavior
  // so I can use my own file request. In this case, I wanted to use a method
  // though I'm not quite sure about this part?
  &lt;el-upload
       action="",
       :http-request="addAttachment",
       :on-remove="deleteAttachment",
       :file-list="attachments"&gt;
       &lt;el-button size="mini" type="primary"&gt;Add file&lt;/el-button&gt;
  &lt;/el-upload&gt;
  
  // button that uploads the files here
  </code></pre>
  
  <p><strong>JS</strong></p>
  
  <pre><code>data() {
       attachments: []
  },
  
  methods: {
       addAttachment ( file, fileList ) {
            this.attachments.push( file );
       },
  
       deleteAttachment () {
            // removes from array
       }
  }
  </code></pre>