TypeScript: TypeError: Cannot assign to read only property 'constructor'

With the TypeScript 1.8 change of 'use strict', the emitted JavaScript (specifically __extends helper) can be invalid.

TypeScript:

import makeError = require('make-error')

export class SubError extends makeError.BaseError {}

Emitted JavaScript:

"use strict";
var __extends = (this && this.__extends) || function (d, b) {
    for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
    function __() { this.constructor = d; }
    d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
var makeError = require('make-error');
var SubError = (function (_super) {
    __extends(SubError, _super);
    function SubError() {
        _super.apply(this, arguments);
    }
    return SubError;
}(makeError.BaseError));
exports.SubError = SubError;

Error:

/Users/blakeembrey/Projects/tmp/test.js:4
    function __() { this.constructor = d; }
                                     ^

TypeError: Cannot assign to read only property 'constructor' of Error
    at BaseError.__ (/Users/blakeembrey/Projects/tmp/test.js:4:38)
    at __extends (/Users/blakeembrey/Projects/tmp/test.js:5:80)
    at /Users/blakeembrey/Projects/tmp/test.js:9:5

About this issue

Original URL
State: closed
Created 8 years ago
Comments: 22 (16 by maintainers)

Commits related to this issue

chore: Lock typescript version to 1.7.5 Typescript 1.8.x can emit invalid JS: https://github.com/Microsoft/TypeScript/issues/6887 — committed to jteplitz/angularfire2 by jteplitz 8 years ago

Most upvoted comments

We would have the same issue if someone were to write the following:

class A {}
Object.freeze(A.prototype);
class B extends A { }

Even with this @blakeembrey’s proposed change, we would still error in the following case:

class A {
  method() {}
}
Object.freeze(A.prototype);
class B extends A { 
  method() {}
}

This is because we assign methods on the prototype, rather than calling Object.defineProperty.

rbuckton on Feb 9, 2016