我最近在 Heroku 上部署了我的 API，但我遇到了一些与 CORS 相关的问题。我已经看到许多其他关于启用 CORS 的帖子（我已经在我的代码中这样做了），但是每当我发出 axios POST 请求时，我仍然遇到相同的错误：Origin http://localhost:3000 is not allowed by Access-Control-Allow-Origin.我也尝试弄乱配置cors() 的对象，但似乎没有任何效果。

来自前端的实际发布请求如下所示：

const axiosConfig = {
        headers: {
          "Content-Type": "multipart/form-data",
          Accept: "application/json",
        },
      };
  await axios
    .post("https://myapp-backend.herokuapp.com/register", data, axiosConfig)
    .then((_) => Message.success("Successfully registered! 🎊"))
    .catch((error) => Message.error(error.message));

我在后端的 app.js 看起来像这样。

const createError = require("http-errors");
const express = require("express");
const path = require("path");
const cookieParser = require("cookie-parser");
const bodyParser = require("body-parser");
const logger = require("morgan");
const multer = require("multer");
const cors = require("cors");

const app = express();
app.use(
  cors({
    allowedHeaders: ["authorization", "Content-Type"], // you can change the headers
    exposedHeaders: ["authorization"], // you can change the headers
    origin: "*",
    methods: "GET,HEAD,PUT,PATCH,POST,DELETE",
    preflightContinue: false,
  })
);

// set up different routers
const indexRouter = require("./routes/index");
const usersRouter = require("./routes/users");
const registrationRouter = require("./registration/routes");
const retailRouter = require("./retail-info/routes");
const bookingRouter = require("./booking/routes");

const port = process.env.PORT || 8080;

const storage = multer.diskStorage({
  destination: function (req, file, cb) {
    if (file.originalname.startsWith("CODE_COVER_QLYag759")) {
      cb(null, "temp-storage/cover/");
    } else {
      cb(null, "temp-storage/");
    }
  },
  filename: function (req, file, cb) {
    cb(null, Date.now() + path.extname(file.originalname)); //Appending extension
  },
});

const upload = multer({
  // dest: "temp-storage/",
  storage: storage,
  limits: {
    fileSize: 5 * 1024 * 1024, // no larger than 5mb, change as needed.
  },
});

// view engine setup

app.use(logger("dev"));
app.use(express.json());
app.use(bodyParser.json());
app.use(express.urlencoded({ extended: false }));
app.use(express.static(path.join(__dirname, "public")));

app.use("/", indexRouter);
app.use("/users", usersRouter);
app.use("/register", upload.any(), registrationRouter);
app.use("/retail", retailRouter);
app.use("/booking", bookingRouter);

// catch 404 and forward to error handler
app.use(function (req, res, next) {
  next(createError(404));
});

// error handler
app.use(function (err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get("env") === "development" ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.json({ error: err.message });
});

app.get("*", (req, res) => {
  res.sendFile(path.resolve(__dirname, "build", "index.html"));
});

app.listen(port, console.log(`MyApp backend started on port ${port}!`));

module.exports = app;

如果有人可以帮助我，我将不胜感激！