TypeScript import gives error importing Express with proper flags

Question

I'm attempting to write an Express server with TypeScript. Everything is written from scratch instead of a CLI, so I'm sure there's an error somewhere in my setup.

I want to write import express, { Application } from express just as I have it in other servers I've written, but I get the error:

import express from 'express'
         ~~~~~~~

  node_modules/@types/express/index.d.ts:115:1
    115 export = e;
        ~~~~~~~~~~~
    This module is declared with using 'export =', and can only be used with a default import when using the 'esModuleInterop' flag.

TS Config:

{
    "compilerOptions": {
      "target": "es5",
      "module": "esnext",
      "moduleResolution": "node",
      "experimentalDecorators": true,
      "allowJs": true,
      "noEmit": true,
      "strict": true,
      "noImplicitAny": true,
      "esModuleInterop": true,
      "allowSyntheticDefaultImports": true,
      "forceConsistentCasingInFileNames": true
    },
    "exclude": [
        "node_modules"
    ]
  }

And the package JSON:

"dependencies": {
    "@types/bcrypt": "^3.0.0",
    "@types/body-parser": "^1.19.0",
    "@types/knex": "^0.16.1",
    "@types/moment": "^2.13.0",
    "bcrypt": "^4.0.1",
    "body-parser": "^1.19.0",
    "dotenv": "^8.2.0",
    "express": "^4.17.1",
    "knex": "^0.20.13",
    "moment": "^2.24.0",
    "pg": "^8.0.0",
    "tsc": "^1.20150623.0",
    "typescript": "^3.8.3"
  },
  "devDependencies": {
    "@babel/cli": "^7.8.4",
    "@babel/core": "^7.9.0",
    "@babel/preset-env": "^7.9.0",
    "@babel/preset-typescript": "^7.9.0",
    "@types/express": "^4.17.4"
  }

Babel is currently unused. I've tried changing module as well with no luck.

Arc · Accepted Answer · 2020-04-04 07:11:44Z

3

The issue is caused by "noEmit": true as that prevents any output, so of course I wasn't seeing any changes after running 'tsc'.

I was seeing errors messages specifically when running tsc server.ts because running with arguments or flags will ignore the tsconfig.json and use default flags, so running tsc server.ts --esModuleInterop produced expected results.

This is why I'm running it all from scratch, so I can make stupid mistakes like this, I guess. Hopefully anyone else who comes across this will have a better understanding of how 'tsc' and 'tsconfig.json' interact with each other.

answered Apr 4, 2020 at 7:11

Arc

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Comments

pyjl · Accepted Answer · 2021-12-21 14:12:07Z

0

I know you already solved this awhile back but wanted to comment - I ran into a similar issue when learning typescript and found this typescript outDir setting in tsconfig.json not working

It looks like maybe just compiling with tsc might be the way to go - it sounds like when we pass in file names like tsc server.ts it ignores the tsconfig.json file.

Typescript Documentation - https://www.typescriptlang.org/docs/handbook/tsconfig-json.html

answered Dec 21, 2021 at 14:12

pyjl

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