Using http-proxy-middleware with typescript and cross-env

Question

I am trying to set up a proxy for my React TypeScript app using http-proxy-middleware to prevent CORS errors while developing.

I have this in my project:

proxy/proxy.tsx

import * as express from 'express'
import { createProxyMiddleware } from 'http-proxy-middleware'

const app = express()

app.use('/api', createProxyMiddleware({ target: 'localhost:8080', changeOrigin: true }))
app.listen(3000)

Then in

package.json

"main": "src/index.tsx",
"scripts": {
  ...
  "proxy": "cross-env nodemon proxy/proxy",
  ...
},

However when I run the script in the console I get this:

[nodemon] starting `node proxy/proxy src/index.tsx`
(node:28564) Warning: To load an ES module, set "type": "module" in the package.json or use the .mjs extension.
C:\*path to project*\pet-project-fe\src\index.tsx:1
import React from 'react'
^^^^^^

SyntaxError: Cannot use import statement outside a module
    at wrapSafe (internal/modules/cjs/loader.js:1053:16)
    at Module._compile (internal/modules/cjs/loader.js:1101:27)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1157:10)
    at Module.load (internal/modules/cjs/loader.js:985:32)
    at Function.Module._load (internal/modules/cjs/loader.js:878:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12)
    at internal/main/run_main_module.js:17:47
[nodemon] app crashed - waiting for file changes before starting...

If I try adding type": "module" to packages.json then my actual app stops running with the error:

"C:\Program Files\nodejs\node.exe" C:\*path to npm*\npm\node_modules\yarn\bin\yarn.js run start
yarn run v1.22.4
$ cross-env NODE_ENV=development webpack-dev-server --open --content-base ./public --port 3001
internal/modules/cjs/loader.js:1153
      throw new ERR_REQUIRE_ESM(filename, parentPath, packageJsonPath);
      ^

Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: C:\*path to project*\pet-project-fe\webpack.config.js
require() of ES modules is not supported.
require() of C:\*path to project*\pet-project-fe\webpack.config.js from C:\*path to project*\pet-project-fe\node_modules\webpack-cli
\bin\utils\convert-argv.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which defines
all .js files in that package scope as ES modules.
Instead rename webpack.config.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from C:\*path to project*\pet-project-fe\package.json.

    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1153:13)
    at Module.load (internal/modules/cjs/loader.js:985:32)
    at Function.Module._load (internal/modules/cjs/loader.js:878:14)
    at Module.require (internal/modules/cjs/loader.js:1025:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at WEBPACK_OPTIONS (C:\*path to project*\pet-project-fe\node_modules\webpack-cli\bin\utils\convert-argv.js:114:13)
    at requireConfig (C:\*path to project*\pet-project-fe\node_modules\webpack-cli\bin\utils\convert-argv.js:116:6)
    at C:\*path to project*\pet-project-fe\node_modules\webpack-cli\bin\utils\convert-argv.js:123:17
    at Array.forEach (<anonymous>)
    at module.exports (C:\*path to project*\pet-project-fe\node_modules\webpack-cli\bin\utils\convert-argv.js:121:15) {
  code: 'ERR_REQUIRE_ESM'
}
error Command failed with exit code 1.

I not even sure what "type" is used for and why its apparently needed in this case, so I don't really want to add random things without knowing what I'm doing. It doesn't solve the problem anyway as I get a new error then when running the proxy:

$ cross-env nodemon proxy/proxy
[nodemon] 2.0.4
[nodemon] to restart at any time, enter `rs`
[nodemon] watching path(s): *.*
[nodemon] watching extensions: tsx,json
[nodemon] starting `node proxy/proxy src/index.tsx`
(node:25420) ExperimentalWarning: The ESM module loader is experimental.
internal/modules/run_main.js:54
    internalBinding('errors').triggerUncaughtException(
                              ^

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".tsx" for C:\*path to project*\pet-project-fe\src\index.tsx
    at Loader.defaultGetFormat [as _getFormat] (internal/modules/esm/get_format.js:65:15)
    at Loader.getFormat (internal/modules/esm/loader.js:113:42)
    at Loader.getModuleJob (internal/modules/esm/loader.js:244:31)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async Loader.import (internal/modules/esm/loader.js:178:17) {
  code: 'ERR_UNKNOWN_FILE_EXTENSION'
}
[nodemon] app crashed - waiting for file changes before starting...

Not sure if this has anything to do with TypeScript, but I thought I'd mention it just in case.

What am I doing wrong here?

Raul Špilev · Accepted Answer · 2020-08-12 19:50:45Z

I finally got it working.

First of all I gave up on trying to get the proxy to work with a .txs filetype. So I went with .js and also used require(...) instead of import

const express = require('express')
const { createProxyMiddleware } = require('http-proxy-middleware')

const app = express()
    
app.use('/api/**', createProxyMiddleware({ target: 'http://localhost:8080', changeOrigin: true }))
app.listen(3002)

Then I realized that this all makes no sense, because if I made a query to ./api it would direct it to the actual apps port, which is port 3001, because that is where my actual app is running at.

"start": "cross-env NODE_ENV=development webpack-dev-server --open --content-base ./public --port 3001",

Making a direct call to port 3002 resulted in a failure and running them both on 3001 stopped my app from working altogether. So the solution was to add this to webpack.config.js:

config.devServer = {
  ...
  proxy: [{
    context: ['/api'],
    target: `http://localhost:3002`,
    changeOrigin: true,
  }],
};

Now hold on a second here. Why am I doing this? Why not just target port 8080 right away here any bypass that proxy.js totally... and what do you know. It works. All I had to do was add

config.devServer = {
  ...
  proxy: [{
    context: ['/api'],
    target: `http://localhost:8080`,
    changeOrigin: true,
  }],
};

to webpack.config.js.

And with that I concede that I have absolutely no idea what I am doing and all of this stuff is very confusing, error-prone and complicated. I was able to remove express and http-middleware-proxy from my dependencies (the dev server seems to get them on their own).

In conclusion I gave up trying to set up my own express proxy, realized that apparently webpack-dev-server already has proxy capabilities, resorted to just using that and left feeling defeated even though I got it working in the end.

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