Invalid left-hand side in assignment

[randalpinto]

What version of Next.js are you using?

11.1.2

What version of Node.js are you using?

12.22.1

What browser are you using?

Chrome

What operating system are you using?

MacOS

How are you deploying your application?

Other platform

Describe the Bug

When packaging up my application for serverless deployment the following code:

https://github.com/vercel/next.js/blob/canary/packages/next/server/next-server.ts#L295

gets packaged up to:

true = JSON.stringify(true);

which results in the following exception at runtime:

"/var/task/chunks/602.js:429285",
        "            true = JSON.stringify(true);",
        "            ^^^^",
        "",
        "SyntaxError: Invalid left-hand side in assignment",
        "    at wrapSafe (internal/modules/cjs/loader.js:988:16)",
        "    at Module._compile (internal/modules/cjs/loader.js:1036:27)",
        "    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1101:10)",
        "    at Module.load (internal/modules/cjs/loader.js:937:32)",
        "    at Function.Module._load (internal/modules/cjs/loader.js:778:12)",
        "    at Module.require (internal/modules/cjs/loader.js:961:19)",
        "    at require (internal/modules/cjs/helpers.js:92:18)",
        "    at Object.__webpack_require__.f.require (/var/task/pages/api/test.js:495:28)",
        "    at /var/task/pages/api/test.js:418:40",
        "    at Array.reduce (<anonymous>)"

Expected Behavior

No exception

To Reproduce

I am deploying my app using: https://github.com/serverless-nextjs/serverless-next.js

A simple API route that returns 200 OK results in this error.

[PatrickChoDev]

isn't true the JavaScript and TypeScript restricted words?
https://www.typescriptlang.org/docs/handbook/2/everyday-types.html

[ijjk]

Hi, this sounds like a bug in how the bundling in serverless-next is being handled as next-server shouldn't be processed with webpack which it sounds like it is since the process.env value is being replaced probably via DefinePlugin which shouldn't be run on next-server.

[randalpinto]

@ijjk the plot thickens, i have tried a completely different serverless deployment method (using AWS amplify) and i get the exact same error. Someone else in the serverless-next issue i opened said:

i had similar, and it had to do with version conflict between next, webpack and typescript. what version of typescript and webpack are being used?

I am using:

"typescript": "4.4.3",
"webpack": "5.56.0",
"next": "11.1.2",

Any ideas?

[randalpinto]

right, after a tortuous path I finally found the culprit. We use Sentry and deep in their docs it says that the webpack configuration is not compatible with serverless environments: https://docs.sentry.io/platforms/javascript/guides/nextjs/manual-setup/. This can be closed.

[zigang93]

after few hour of investigation,
middleware.ts will broken when your next.config.js have webpack config like this below:

remove the config will start your middleware..
@ijjk any other solution to have build ID ? I want notify user when new build was deploy to docker

//  next.config.js
webpack: (config, { buildId }) => {
    config.plugins.push(
      new webpack.DefinePlugin({
        'process.env': {
          BUILD_ID: JSON.stringify(buildId),
        },
      })
    )
    return config
  },

[KosGrillis]

I can confirm that this is the culprit. Does any one have any fixes for this?

[favll]

Simply rewriting the key for the DefinePlugin was enough to fix the issue for me.

    config.plugins.push(
      new webpack.DefinePlugin({
        "process.env.BUILD_ID": JSON.stringify(buildId),
      })
    );

This is probably due to how the DefinePlugin works. To quote the docs:

When defining values for process prefer 'process.env.NODE_ENV': JSON.stringify('production') over process: { env: { NODE_ENV: JSON.stringify('production') } }. Using the latter will overwrite the process object which can break compatibility with some modules that expect other values on the process object to be defined.

[maxnowack]

Thanks, @favll! This has done the trick for me as well