vue+axios+el-upload实现文件上传并跨域

要实现Vue + Axios + El-upload进行文件上传并跨域，需要按照以下步骤进行操作：

1. 在Vue项目中安装axios和element-ui。在命令行中输入以下命令即可安装：

   npm install axios element-ui --save

2. 在Vue项目中创建一个上传文件的组件，例如FileUpload.vue。在该组件中导入axios和element-ui，并且引入El-upload组件。示例代码如下：

   <template>
     <div>
       <el-upload
         class="upload-demo"
         :action="uploadUrl"
         :on-success="handleUploadSuccess"
         :before-upload="beforeUpload"
         :headers="headers"
         :data="formData"
         :file-list="fileList">
         <el-button size="small" type="primary">点击上传</el-button>
       </el-upload>
     </div>
   </template>
   
   <script>
   import axios from 'axios'
   import { Message } from 'element-ui'
   
   export default {
     name: 'FileUpload',
     data () {
       return {
         fileList: [],
         uploadUrl: 'http://example.com/upload',
         formData: {},
         headers: {
           'Content-Type': 'multipart/form-data'
         }
       }
     },
     methods: {
       handleUploadSuccess (response, file, fileList) {
         // 上传成功后的处理逻辑
         console.log(response)
       },
       beforeUpload (file) {
         // 文件上传前的处理逻辑
         console.log(file)
       }
     }
   }
   </script>

3. 在组件中实现文件上传的逻辑。在上传文件之前，需要设置请求头和请求数据，并且需要处理跨域请求。可以在组件的methods中定义一个upload方法，用来发送上传请求。示例代码如下：

   <script>
   import axios from 'axios'
   import { Message } from 'element-ui'
   
   export default {
     name: 'FileUpload',
     data () {
       return {
         fileList: [],
         uploadUrl: 'http://example.com/upload',
         formData: {},
         headers: {
           'Content-Type': 'multipart/form-data'
         }
       }
     },
     methods: {
       handleUploadSuccess (response, file, fileList) {
         // 上传成功后的处理逻辑
         console.log(response)
       },
       beforeUpload (file) {
         // 文件上传前的处理逻辑
         console.log(file)
       },
       upload () {
         let config = {
           headers: this.headers,
           withCredentials: true // 跨域请求需要设置withCredentials为true
         }
         let data = new FormData()
         data.append('file', this.fileList[0].raw)
         // 向后端发送上传请求
         axios.post(this.uploadUrl, data, config)
           .then(response => {
             this.handleUploadSuccess(response)
           })
           .catch(error => {
             console.log(error)
           })
       }
     }
   }
   </script>

4. 最后，在Vue组件中使用El-upload组件，并且调用upload方法即可实现文件上传。示例代码如下：

   <template>
     <div>
       <el-upload
         class="upload-demo"
         :action="uploadUrl"
         :on-success="handleUploadSuccess"
         :before-upload="beforeUpload"
         :headers="headers"
         :data="formData"
         :file-list="fileList">
         <el-button size="small" type="primary" @click="upload">点击上传</el-button>
       </el-upload>
     </div>
   </template>
   
   <script>
   import axios from 'axios'
   import { Message } from 'element-ui'
   
   export default {
     name: 'FileUpload',
     data () {
       return {
         fileList: [],
         uploadUrl: 'http://example.com/upload',
         formData: {},
         headers: {
           'Content-Type': 'multipart/form-data'
         }
       }
     },
     methods: {
       handleUploadSuccess (response, file, fileList) {
         // 上传成功后的处理逻辑
         console.log(response)
       },
       beforeUpload (file) {
         // 文件上传前的处理逻辑
         console.log(file)
       },
       upload () {
         let config = {
           headers: this.headers,
           withCredentials: true // 跨域请求需要设置withCredentials为true
         }
         let data = new FormData()
         data.append('file', this.fileList[0].raw)
         // 向后端发送上传请求
         axios.post(this.uploadUrl, data, config)
           .then(response => {
             this.handleUploadSuccess(response)
           })
           .catch(error => {
             console.log(error)
           })
       }
     }
   }
   </script>