Check if property descriptor is configurable before re-defining it

[jdelStrother]

Android Browser 4.0 appears to have a non-configurable Error.prototype.name property -

Object.getOwnPropertyDescriptor(Error.prototype, 'name')
// returns - 
{"value":"Error", "writable": false, "enumerable": false, "configurable": false}

and will raise a (confusingly-name) "Cannot redefine property: defineProperty" error if you try to re-define Error.prototype.name.

How about checking for desc.configurable before attempting to call Object.defineProperty ?

This fixes #373

[ljharb]

Hmm - while I think this is a good fix, that property descriptor says it's not enumerable. What does Object.prototype.propertyIsEnumerable.call(Error.prototype, 'name') say on Android Browser 4.0?

[jdelStrother]

Ugh, sorry - I've been limited to debugging this via lots of alert()s, and had to manually copy that message across - I must have typoed it. The real value is :

Object.getOwnPropertyDescriptor(Error.prototype, 'name')
// returns - 
{"value":"Error", "writable": false, "enumerable": true, "configurable": false}

(and FWIW, yes, Object.prototype.propertyIsEnumerable.call(Error.prototype, 'name') returns true)

[ljharb]

Phew, ok, at least they're consistent :-D That would be far worse. Thanks!

I'll merge and release this as soon as I can verify it on Browserstack - hopefully later today, or if not, tomorrow.