TypeError: Cannot assign to read only property 'toJSON' of object 'Error'

• Operating System version: macos 10.12.6, Node 9.5.0
• Firebase SDK version: 5.9.0
• Library version: 4.10.1
• Firebase Product: admin (auth, database, storage, etc)

[REQUIRED] Step 3: Describe the problem

Installed firebase-admin using instructions here: https://www.npmjs.com/package/firebase-admin Added firebase-admin to a module as instructed using:

var admin = require('firebase-admin');

in a module in a loopback node application. Application fails to start with the following error:

/Users/simon/Projects/APPICS/src/appics-backend/node_modules/firebase-admin/lib/utils/error.js:65
    FirebaseError.prototype.toJSON = function () {
                                   ^

TypeError: Cannot assign to read only property 'toJSON' of object 'Error'
    at /Users/abcdefg/Projects/APPICS/src/appics-backend/node_modules/firebase-admin/lib/utils/error.js:65:36
    at Object.<anonymous> (/Users/simon/Projects/APPICS/src/appics-backend/node_modules/firebase-admin/lib/utils/error.js:72:2)
    at Module._compile (module.js:660:30)
    at Object.Module._extensions..js (module.js:671:10)
    at Module.load (module.js:573:32)
    at tryModuleLoad (module.js:513:12)
    at Function.Module._load (module.js:505:3)
    at Module.require (module.js:604:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/Users/abcdefg/Projects/APPICS/src/appics-backend/node_modules/firebase-admin/lib/firebase-namespace.js:21:15)
    at Module._compile (module.js:660:30)
    at Object.Module._extensions..js (module.js:671:10)
    at Module.load (module.js:573:32)
    at tryModuleLoad (module.js:513:12)
    at Function.Module._load (module.js:505:3)
    at Module.require (module.js:604:17)
Waiting for the debugger to disconnect...

Process finished with exit code 1

Steps to reproduce:

What happened? How can we make the problem occur? This could be a description, log/console output, etc.

Relevant Code:

'use strict';

let admin = require("firebase-admin");

[abdurahmanadilovic]

I used this command to figure out where toJSON is defined as a read only property on Error objects

grep -r 'Object.defineProperty(Error.*' .

It was in my application code and not in any package. I just added writable: true to Object.assignProperty call and that fixed the issue. This is the code after modification:

Object.defineProperty(Error.prototype, 'toJSON', {
  value() {
    const alt = {};

    Object.getOwnPropertyNames(this).forEach(function (key) {
      alt[key] = this[key];
    }, this);

    return alt;
  },
  configurable: true,
  writable: true
});

@JuergenSimon, @reactor81 can you please run the grep command and check where is toJSON defined as a read only property?

[hiranya911]

Hey @abdurahmanadilovic. Do you have a repro for this issue? Ideally something that just uses TypeScript and no other frameworks? The original reporter of this issue could only repro the problem on Loopback.