"Cannot read property 'upgrade' of undefined" when starting vue application

Question

I have a project that's been running perfectly for a few months now, able to run npm run serve with no problem. I have to terminate and run the command again whenever I switch networks, but that has never been a problem and the server could always start again.

Until now - no matter what I do I can't get the server to start. I get this error:

npm run serve

> [email protected] serve D:\workspace\[PROJECT]
> vue-cli-service serve

 INFO  Starting development server...
 10% building 1/1 modules 0 active ERROR  TypeError: Cannot read property 'upgrade' of undefined
TypeError: Cannot read property 'upgrade' of undefined
    at Server.<anonymous> (D:\workspace\[PROJECT]\node_modules\webpack-dev-server\lib\Server.js:667:47)
    at Array.forEach (<anonymous>)
    at new Server (D:\workspace\[PROJECT]\node_modules\webpack-dev-server\lib\Server.js:666:22)
    at serve (D:\workspace\[PROJECT]\node_modules\@vue\cli-service\lib\commands\serve.js:137:20)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)
    at Function.Module.runMain (module.js:695:11)
    at startup (bootstrap_node.js:191:16)
    at bootstrap_node.js:612:3

The last time I got this message was when I forgot to set the .env files, but this is a previously working copy with all necessary files set, and no changes since the last working run.

I've even tried pulling a fresh copy of the repo, running npm i and setting all env files but it still fails.

npm run lint and npm run build can still work, only npm run serve.

Am I missing anything?

Answer 1

The problem was again with the .env files. My vue.config.js was trying to access a previously set environment variable that had since been removed.

Only strange thing was that there weren't any problems up til now?

Answer 2

I guess your devServer.proxy.target is empty! You could set this configuration

Answer 3

For me it was that I forgot to create (or copy from another PC) the .env file after clone and try to run my project on another PC.

Answer 4

I also had this problem.

I used in the project process to get the backend address(for example):

  devServer: {
    proxy: {
      '/api/back/*': {
        target: process.env.VUE_APP_BACKEND_URL,
        pathRewrite: {
          '/api/back': '/api/back',
        },
      },
    },
  },

But there was no .evn file.

Just create .env file:

VUE_APP_BACKEND_URL= 0.0.0.0:2222 #example

Didn't notice the answer @Sergey.