废话少说，直接代码
app.js
const Koa = require('koa')
const body = require('koa-better-body')
const path = require('path')
const static = require('koa-static')
const app = new Koa()
app.use(body({
uploadDir: path.resolve(__dirname, "./upload")
}))
app.use(static(path.resolve('./upload')))
app.use(async ctx => {
console.log(ctx.request.fields)
ctx.body = "以一当十，是我精神"
})
app.listen(3000)index.html:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<form action="http://localhost:3000" method="post" enctype="multipart/form-data">
username: <input type="text" name="username" /> <br>
passoword: <input type="text" name="psw" /> <br>
image <input type="file">
<input type="submit" value="submit">
</form>
</body>
</html>发现图片没上传成功，
有时候真的，就这么一丁点问题，不信，你试试！