[REGRESSION] Cannot assign to read only property '__esModule' of object

[appsforartists]

TypeScript Version: 2.2.1

Code

// presuming react-router@4.0.0-alpha.6 is installed
import Link from 'react-router/Link';

Note: Using pundle@2.0.0-beta12 to do bundling

tsconfig.json

{
  "compilerOptions": {
    "declaration": true,
    "lib": [
      "es2015",
      "es2016",
      "es2017",
      "dom"
    ],
    "importHelpers": true,
    "module": "commonjs",
    "moduleResolution": "node",
    "noImplicitAny": true,
    "noImplicitThis": true,
    "sourceMap": true,
    "strictNullChecks": true,
    "target": "es6"
  }
}

Expected behavior:

Link is imported to the local namespace.

Actual behavior:

Uncaught TypeError: Cannot assign to read only property '__esModule' of object '#<Object>'
    at Object.<anonymous> (Link.js:3)

in Chrome 56.0.2924.87. Reverting to TypeScript@2.1.6 solves the issue.

[mhegazy]

__esModule property is emitted by the compiler in any ES6 module. This tells other transpiles that this module follows the ES6 module semantics and not a CommonJS/AMD module.

Why are you assigning to __esModule property?

[appsforartists]

I'm not - tsc is.

[mhegazy]

Can you share a self contained sample showing the issue?

[appsforartists]

Looks like this might be an incompatibility between TS@2.2 and Babel. As you can see, Babel is defining __esModule:true in its exports:

• in react-router
• in a web repl

I had surmised that tsc had changed its behavior around __esModule since this is a regression in 2.2, but upon investigating further, I see that __esModule is present in packages that have been built with babel and published to npm.

[appsforartists]

Let me know if this is helpful; otherwise, I can delete it:

https://github.com/material-motion/tsc-reduction

[mhegazy]

What do i need to run to trigger the error?

[appsforartists]

I just pushed a sample page to that repo. Pull the latest and run yarn run start, then open it in Chrome.

[mhegazy]

Looks like your loader is calling the ts compiler on a .js file ("$app/node_modules/react-router/Link.js) that has already been transformed. not sure why though.

[appsforartists]

Sounds like it's mostly a configuration issue, though it's bizarre that it worked and now it doesn't. Did TS2.2 make meaningful changes to __esModule? That's not listed in https://github.com/Microsoft/TypeScript/wiki/What%27s-new-in-TypeScript

[mhegazy]

yes. In TS 2.1 __esModule was only emitted in modules that had a default export, in TS 2.2 __esModule for all modules.

[appsforartists]

@DanielRosenwasser - you were interested in this.