Koa 提交和接收 JSON 表单数据

来自 url 中的 query 参数可直接通过 context.query 获取，但 POST 方式提交的表单数据则需要借助中间件的解析来完成，比如 koa-bodyparser。

首先准备好一个表单页面，为了演示，其中包含一个数组类型的数据。

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>post json</title>
  </head>
  <body>
    <form action="/save" method="POST">
      <div>
        <label for="name"
          >name:
          <input type="text" name="name" id="name" value="Tom" />
        </label>
      </div>
      <div>
        <label for="age"
          >age:
          <input type="number" name="age" id="age" value="19" />
        </label>
      </div>
      <div>
        <label
          >hobbies:
          <br />
          <input
            type="text"
            name="hobbies[0]"
            id="hobbies[0]"
            value="reading"
          />
          <br />
          <input type="text" name="hobbies[1]" id="hobbies[1]" value="music" />
          <br />
          <input type="text" name="hobbies[2]" id="hobbies[2]" value="swim" />
        </label>
      </div>
      <button type="submit">Submit</button>
    </form>
  </body>
</html>

server.js

var Koa = require("koa");
var Router = require("koa-router");
var fs = require("fs");
var bodyParser = require("koa-bodyparser");
var app = new Koa();

var router = new Router();
app.use(bodyParser());
router.get("/", async (ctx, next) => {

ctx.type = "html";

ctx.body = fs.createReadStream("index.html");

});
router.post("/save", async (ctx, next) => {

ctx.body = ctx.request.body;

});
app.use(router.routes()).use(router.allowedMethods());

app.listen(3000);
console.log("server started at http:localhost:3000");

通过 Node.js 调试模式启动服务可查看到接收到的数据，其中数据类型解析正常。

$ node --inspect-brk server.js
server started

接收到的表单数据

但其实前台页面提交的并不是 JSON 类型，这是 koa-bodyparse 解析后的结果。通过 Chrome Devtools 的网络面板可看到，真实的类型为 Request 中 Content-Type 字段，为 application/x-www-form-urlencoded。

表单提交时的请求类型为 `application/x-www-form-urlencoded`

原生的 HTML 表单 <form> 是没有 JSON 类型的，其总共有三种默认的格式，

application/x-www-form-urlencoded
multipart/form-data
text/plain

默认为 application/x-www-form-urlencoded，可通过 <form> 表单的 enctype 指定。

所以真正意义上以 JSON 格式提交，需要借助 JavaScript，真实场景下表单也大多会走代码提交而非原生 submit 类型的 <button>。

首页更新表单代码添加 onsubmit 方法：

- <form action="/save" method="POST">
+ <form action="/save" method="POST" onsubmit="submitForm(event)" id="myForm">

添加以下代码到页面以提交表单：

<script>
    function submitForm(event) {
        event.preventDefault();
        var formData = new FormData(myForm);
        let data = {};
        for (var [key, value] of formData.entries()) {
            if (key.startsWith("hobbies")) {
            data["hobbies"]
                ? data["hobbies"].push(value)
                : (data["hobbies"] = [value]);
            } else {
            data[key] = value;
            }
        }
    <span class="pl-en">fetch</span>(<span class="pl-s"><span class="pl-pds">"</span>/save<span class="pl-pds">"</span></span>, {
        method<span class="pl-k">:</span> <span class="pl-s"><span class="pl-pds">"</span>POST<span class="pl-pds">"</span></span>,
        headers<span class="pl-k">:</span> {
        <span class="pl-s"><span class="pl-pds">"</span>Content-Type<span class="pl-pds">"</span></span><span class="pl-k">:</span> <span class="pl-s"><span class="pl-pds">"</span>application/json<span class="pl-pds">"</span></span>
        },
        body<span class="pl-k">:</span> <span class="pl-c1">JSON</span>.<span class="pl-c1">stringify</span>(data)
    })
        .<span class="pl-c1">then</span>(<span class="pl-k">function</span>(<span class="pl-smi">response</span>) {
        <span class="pl-k">return</span> <span class="pl-smi">response</span>.<span class="pl-en">json</span>();
        })
        .<span class="pl-c1">then</span>(<span class="pl-k">function</span>(<span class="pl-smi">response</span>) {
        <span class="pl-en">console</span>.<span class="pl-c1">log</span>(response);
        });
}

</script>

最后完整的后台与页面代码为：

server.js

var Koa = require("koa");
var Router = require("koa-router");
var fs = require("fs");
var bodyParser = require("koa-bodyparser");
var app = new Koa();

var router = new Router();
app.use(bodyParser());
router.get("/", async (ctx, next) => {

ctx.type = "html";

ctx.body = fs.createReadStream("index.html");

});
router.post("/save", async (ctx, next) => {

ctx.body = ctx.request.body;

});
app.use(router.routes()).use(router.allowedMethods());

app.listen(3000);
console.log("server started at http:localhost:3000");

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>post json</title>
  </head>
  <body>
    <form action="/save" method="POST" onsubmit="submitForm(event)" id="myForm">
      <div>
        <label for="name"
          >name:
          <input type="text" name="name" id="name" value="Tom" />
        </label>
      </div>
      <div>
        <label for="age"
          >age:
          <input type="number" name="age" id="age" value="19" />
        </label>
      </div>
      <div>
        <label
          >hobbies:
          <br />
          <input
            type="text"
            name="hobbies[0]"
            id="hobbies[0]"
            value="reading"
          />
          <br />
          <input type="text" name="hobbies[1]" id="hobbies[1]" value="music" />
          <br />
          <input type="text" name="hobbies[2]" id="hobbies[2]" value="swim" />
        </label>
      </div>
      <button type="submit">Submit</button>
    </form>
    <script>
      function submitForm(event) {
        event.preventDefault();
        var formData = new FormData(myForm);
        let data = {};
        for (var [key, value] of formData.entries()) {
          if (key.startsWith("hobbies")) {
            data["hobbies"]
              ? data["hobbies"].push(value)
              : (data["hobbies"] = [value]);
          } else {
            data[key] = value;
          }
        }

        fetch("/save", {
          method: "POST",
          headers: {
            "Content-Type": "application/json"
          },
          body: JSON.stringify(data)
        })
          .then(function(response) {
            return response.json();
          })
          .then(function(response) {
            console.log(response);
          });
      }
    </script>
  </body>
</html>

再次查看提交时的 Content-Type 及所提交的数据，已经是 JSON 格式了。

通过 fetch 提交 JSON 格式的表单数据