TypeError: Cannot read property 'dimensions' of undefined

[SpeckyYT]

OS: Windows 7
NodeJS Version: v13.12.0
MathJS Version: v7.0.0 (tested with v6.6.5 too)

I created a prototype for the Object type.

Object.prototype.test = function(){}; // example

But when I require 'mathjs' with that custom prototype, it returns the following error:

TypeError: Cannot read property 'dimensions' of undefined
    at createUnitClass.isClass (%mainpath%\node_modules\mathjs\lib\type\unit\Unit.js:3661:33)
    at assertAndCreate (%mainpath%\node_modules\mathjs\lib\utils\factory.js:49:12)
    at Object.<anonymous> (%mainpath%\node_modules\mathjs\lib\entry\pureFunctionsAny.generated.js:1209:61)
    at Module._compile (internal/modules/cjs/loader.js:1147:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1167:10)
    at Module.load (internal/modules/cjs/loader.js:996:32)
    at Function.Module._load (internal/modules/cjs/loader.js:896:14)
    at Module.require (internal/modules/cjs/loader.js:1036:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at Object.<anonymous> (%mainpath%\node_modules\mathjs\lib\entry\mainAny.js:53:25)
    at Module._compile (internal/modules/cjs/loader.js:1147:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1167:10)
    at Module.load (internal/modules/cjs/loader.js:996:32)
    at Function.Module._load (internal/modules/cjs/loader.js:896:14)
    at Module.require (internal/modules/cjs/loader.js:1036:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at Object.<anonymous> (%mainpath%\node_modules\mathjs\main\es5\index.js:1:18)
    at Module._compile (internal/modules/cjs/loader.js:1147:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1167:10)
    at Module.load (internal/modules/cjs/loader.js:996:32)
    at Function.Module._load (internal/modules/cjs/loader.js:896:14)
    at Module.require (internal/modules/cjs/loader.js:1036:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at Object.<anonymous> (%mainpath%\src\commands\utilities\math.js:10:22)
    at Module._compile (internal/modules/cjs/loader.js:1147:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1167:10)
    at Module.load (internal/modules/cjs/loader.js:996:32)
    at Function.Module._load (internal/modules/cjs/loader.js:896:14)
    at Module.require (internal/modules/cjs/loader.js:1036:19)
    at require (internal/modules/cjs/helpers.js:72:18)

I tried to delete the prototype, and when requiring 'mathjs', it doesn't return any error, but I would need to have those custom prototypes.

I tried to reinstall the 'mathjs' module, but without any success

#535

[josdejong]

Thanks for bringing this up @SpeckyYT . Turns out the library is not robust against Object prototype pollution. I've made a fix for this in #1860, awaiting to see if all tests pass.

Note that it's good practice to never extend the Object prototype! It can very easily break libraries (like you've seen with mathjs), and messing with the Object prototype is a technique often used in attacks. To write a proper unit test to test this, I had to disable eslint for the test because it throws an error when extending the Object prototype.

[josdejong]

Fix is published in v7.0.1