multer中间件上传文件

上传图片中间件 multer

//1.基本语法
npm i multer -S
const multer = require('multer')
const storage = multer.diskStorage({
    destination: function (req, file, cb) {
      cb(null, './public/uploads')
    },
    filename: function (req, file, cb) {
        console.log(file)
        let originalName = file.originalname;
        let ext = originalName.split('.');
        ext= ext[ext.length-1]
      cb(null, file.fieldname + '-' + Date.now()+'.'+ext)
    }
  })
   
const upload = multer({ storage: storage })

router.post('/upload',upload.single('img'),(req,res)=>{
    res.send({
        code:0,
        msg:"上传成功"
    })
})

2.html中form表单中传输文件一定要加入enctype=“multipart/formdata”

<form action="" method="post" enctype="multipart/formdata">
    <input/>
 </form>

实例

创建upload.js upload.ejs app.js uploads(接收图片) 
npm i express body-parser ejs multer -S
首先：在app.js中

const express = require('express');
const bodyParser = require('body-parser');
const path = require('path');

const app = express()
const uploadRouter = require('./routes/upload');
const { urlencoded } = require('body-parser');
//设置post解析
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended:false}))
//设置views
app.set("views",path.join(__dirname,"/views"))
app.set("view engine","ejs")
//使用上传中间件
app.use(uploadRouter)
app.listen(3210,()=>{
    console.log("start at port 3210")
})

2,upload.js中

const router = require('express').Router();
const multer  = require('multer')
const storage = multer.diskStorage({
    //有两个函数，第一个函数是定义存储位置，需要提前创建好文件夹,第二个函数定义文件名.
  destination: function (req, file, cb) {
    cb(null, './public/uploads')
  },
  filename: function (req, file, cb) {
    console.log(file)
    // 处理文件后缀名
    let fileArr = file.originalname.split('.')
    cb(null, file.fieldname + '-' + Date.now()+'.'+fileArr[fileArr.length-1])
  }
})

const upload = multer({ storage: storage })
//首先获取下载页面
router.get("/upload",(req,res)=>{
    res.render("upload")
})

//上传文件的路由，三个参数,中间参数的参数是上传文件的name值
router.post("/upload",upload.single('img'),(req,res)=>{
    res.send({
        code:0,
        msg:'上传成功'
      })
})

module.exports = router

3.upload.ejs文件内容用来传输post数据

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title></title>
    <link rel="stylesheet" href=" ">
    <link rel="stylesheet" href=" ">
</head>
<body>
    <form action="/upload" method="post" enctype="multipart/form-data">
    <!--数以传输文件时必须要加enctype，文件输入框要加name属性-->
        <input type="file" name="img" id='file'>
        <img src="" alt="" id="img">
        <input type="submit" value="提交">
    </form>
</body>
<script type="text/javascript" src="" ></script>
<script type="text/javascript">
    
</script>
</html>

封装upload

1.一般新建文件夹utils存放自己封装的模块，创建upload.js

const multer  = require('multer')
const storage = multer.diskStorage({
    //有两个函数，第一个函数是定义存储位置，需要提前创建好文件夹,第二个函数定义文件名.
  destination: function (req, file, cb) {
    cb(null, './public/uploads')
  },
  filename: function (req, file, cb) {
    console.log(file)
    // 处理文件后缀名
    let fileArr = file.originalname.split('.')
    cb(null, file.fieldname + '-' + Date.now()+'.'+fileArr[fileArr.length-1])
  }
})

const upload = multer({ storage: storage })
//导出
module.exports = upload

2.routes中upload文件引入

const router = require('express').Router();

//引入封装好的上传文件,注意路径需要../,这里是router目录下的文件引入使用的
const upload = require('../utils/upload.js');

//首先获取下载页面
router.get("/upload",(req,res)=>{
    res.render("upload")
})

//上传文件的路由，三个参数,中间参数的参数是上传文件的name值
router.post("/upload",upload.single('img'),(req,res)=>{
    res.send({
        code:0,
        msg:'上传成功'
      })
})

module.exports = router

3.upload.ejs中上传图片预览

<script>
   var file = document.querySelector('#file');
   var oImg = document.querySelector('#img')
   file.onchange = function(){
       // 有个files属性
       console.log(this.files[0])
       var reader = new FileReader();
       reader.readAsDataURL(this.files[0]);
       //异步操作，需要监听
       reader.onload  = function(){
       // 监听 reader 读取文件的进度，当读取完毕时触发
       console.log(this.result)
       oImg.src = this.result
  	}
  }
</script>