Type error: Re-exporting a type when the '--isolatedModules' flag is provided requires using 'export type'

[YoungMahesh]

Hi! 👋

Firstly, thanks for your work on this project! 🙂

I got this error from typescript while creating build version of nextjs. ( I am using 5.5.1 version of ethers on Ubuntu 20.04 LTS )

npm run build

> build
> next build

./node_modules/ethers/src.ts/ethers.ts:96:5
Type error: Re-exporting a type when the '--isolatedModules' flag is provided requires using 'export type'.

  94 |     // Types
  95 | 
> 96 |     ContractFunction,
     |     ^
  97 |     ContractReceipt,
  98 |     ContractTransaction,
  99 |     Event,
info  - Checking validity of types 

And here is the diff that solved my problem:

diff --git a/node_modules/ethers/src.ts/ethers.ts b/node_modules/ethers/src.ts/ethers.ts
index f192c6d..899f802 100644
--- a/node_modules/ethers/src.ts/ethers.ts
+++ b/node_modules/ethers/src.ts/ethers.ts

@@ -58,7 +58,7 @@ 

-export {
+export type {
     Signer,
 
     Wallet,
diff --git a/node_modules/ethers/src.ts/index.ts b/node_modules/ethers/src.ts/index.ts
index b1071dd..1622084 100644
--- a/node_modules/ethers/src.ts/index.ts
+++ b/node_modules/ethers/src.ts/index.ts
@@ -14,7 +14,7 @@ 
 
-export {
+export type {
     Signer,
 
     Wallet,
diff --git a/node_modules/ethers/src.ts/utils.ts b/node_modules/ethers/src.ts/utils.ts
index 7a4de87..e8f32e4 100644
--- a/node_modules/ethers/src.ts/utils.ts
+++ b/node_modules/ethers/src.ts/utils.ts
 
-export {
+export type {
     AbiCoder,
     defaultAbiCoder,
 

This issue body was partially generated by patch-package.

[ricmoo]

Thanks! Glad you like it. :)

It’s definitely not safe to export the objects as types though, as that would mean you cannot use them as values, which the classes and variables are.

What version of TypeScript are you using? What is the purpose of isolateModules? I’ve not ever used that flag.

[YoungMahesh]

Thank you for the reply @ricmoo

My node_modules have tyescript version 4.5.2, which was automatically downloaded by nextjs.

The --isolateModules flag is I think beacuse of because of "isolatedModules": true, inside my tsconfig.json. I made it false but it became true automatically when I run npm run build with printing following statement in console:

We detected TypeScript in your project and reconfigured your tsconfig.json file for you. Strict-mode is set to false by default.

The following mandatory changes were made to your tsconfig.json:

        - isolatedModules was set to true (requirement for SWC / Babel)

This is my tsconfig.json file (auto-generated by nextjs)

{
  "compilerOptions": {
    "target": "es5",
    "lib": [
      "dom",
      "dom.iterable",
      "esnext"
    ],
    "allowJs": true,
    "skipLibCheck": true,
    "strict": false,
    "forceConsistentCasingInFileNames": true,
    "noEmit": true,
    "incremental": true,
    "esModuleInterop": true,
    "module": "esnext",
    "moduleResolution": "node",
    "resolveJsonModule": true,
    "isolatedModules": true,
    "jsx": "preserve"
  },
  "include": [
    "next-env.d.ts",
    "**/*.ts",
    "**/*.tsx",
  ],
  "exclude": [
    "node_modules"
  ]
}

And here is my package.json file

{
  "name": "eth-tools",
  "private": true,
  "scripts": {
    "dev": "next dev",
    "build": "next build",
    "start": "next start",
    "lint": "next lint",
    "postinstall": "patch-package"
  },
  "dependencies": {
    "@emotion/react": "^11.7.0",
    "@emotion/styled": "^11.6.0",
    "@fontsource/roboto": "^4.5.1",
    "@mui/icons-material": "^5.2.0",
    "@mui/lab": "^5.0.0-alpha.58",
    "@mui/material": "^5.2.1",
    "@openzeppelin/contracts": "^4.4.0",
    "date-fns": "^2.27.0",
    "dotenv": "^10.0.0",
    "hardhat": "^2.7.0",
    "next": "12.0.4",
    "patch-package": "^6.4.7",
    "react": "17.0.2",
    "react-dom": "17.0.2"
  },
  "devDependencies": {
    "@nomiclabs/hardhat-ethers": "^2.0.2",
    "@nomiclabs/hardhat-etherscan": "^2.1.8",
    "@nomiclabs/hardhat-waffle": "^2.0.1",
    "chai": "^4.3.4",
    "eslint": "7.32.0",
    "eslint-config-next": "12.0.4",
    "ethereum-waffle": "^3.4.0",
    "ethers": "^5.5.1"
  }
}

[ricmoo]

It looks like it is supposed to be false, but can you try adding the export {} suggested here to your tests? It seems like an issue with your importing-side not understanding something is a module and not a legacy script.

[YoungMahesh]

I am using test files with mocha-syntax as mentioned in the above stackoverflow-page you mentioned.

I put export {} at the end of one of the test files and when I ran npx hardhat test, I got this error:

export { }
^^^^^^

SyntaxError: Unexpected token 'export'`

I used import statement instead of require inside my test-file but it gave this error: SyntaxError: Cannot use import statement outside a module on npx hardhat test.

I also put tsconfig.json with content as:

{
  "extends": "../tsconfig.json",
  "compilerOptions": {
    "isolatedModules": false
  },
}

inside my test folder as mentioned in the second most popular answer on the stackoverflow-page you mentioned above, but the npm run build gave the same isolateModules error.

I am using .js files for hardhat-testing inside test folder.

[ricmoo]

You might need to ping Hardhat for this problem. I don’t think it’s anything ethers can solve. :s

[YoungMahesh]

OK, thank you for the help.

[ghost]

import type { Contract } from "ethers/src.ts/index";
I was fix by remove to import type { Contract } from "ethers";
dont know why. may be this help for another one else