does not work with babel-plugin-transform-builtin-extend

I’ve got a source file, myError.js, being transpiled with babel-plugin-transform-builtin-extend:

export default class MyError extends Error {
    constructor() {
        super('this is a MyError');
    }
}

{
  "presets": [
    [ "es2015" ]
  ],
  "plugins": [
    [ "transform-builtin-extend", {
      "globals": [ "Error" ]
    } ]
  ]
}

the result is a file containing this:

/* _classCallCheck, _possibleConstructorReturn, etc. omitted for brevity... */

function _extendableBuiltin(cls) {
  /* some magic provided by transform-builtin-extend */
  // ...
}

var MyError = function (_extendableBuiltin2) {
    _inherits(MyError, _extendableBuiltin2);

    function MyError() {
        _classCallCheck(this, MyError);

        return _possibleConstructorReturn(this, (MyError.__proto__ || Object.getPrototypeOf(MyError)).call(this, "this is a MyError"));
    }

    return MyError;
}(_extendableBuiltin(Error));

But when I add istanbul to my list of plugins in .babelrc…

  "plugins": [
    [ "transform-builtin-extend", {
      "globals": [ "Error" ]
-    } ]
+   } ],
+  [ "istanbul" ]
  ]

…some of the code generated by transform-builtin-extend seems to be missing:

/* _classCallCheck and friends are still present */

/* the '_extendableBuiltin' function is now gone :( */

var MyError = function (_ref) {
    _inherits(MyError, _ref);

    function MyError() {
        _classCallCheck(this, MyError);

        cov_1jzxyjd0v8.f[0]++;
        cov_1jzxyjd0v8.s[0]++;
        return _possibleConstructorReturn(this, (MyError.__proto__ || Object.getPrototypeOf(MyError)).call(this, "this is a MyError"));
    }

    return MyError;
}((Error)) // <-- no longer a function call, but instead an object reference

Applying istanbul without transform-builtin-extend results in the same output as described above; rearranging the order of my babel plugins does too.

I suspect the problem might be somewhere in istanbul-lib-instrument as that’s where the visitor enter and exit functions are built? But I’m not 100% sure.

I’m running node 8.9.3 with these packages:

 "dependencies": {
    "babel-cli": "^6.26.0",
    "babel-core": "^6.26.0",
    "babel-plugin-istanbul": "^4.1.5",
    "babel-plugin-transform-builtin-extend": "^1.1.2",
    "babel-preset-es2015": "^6.24.1",
    "jest": "^22.0.3"
  }

thanks for any help you can provide!

[kgregory]

There is a workaround for this issue.

Use babel-plugin-transform-builtin-extend, but for any subclasses extending built-ins like Error or Array, you need to explicitly define constructor and __proto__, as described by @xpl in this issue comment.

[tomaswitek]

Is there a workaround for babel 7? The workarounds mentioned above don’t seem to work 😦