Do not mutate user-supplied opts

[vcheung-stripe]

Summary

When a user supplies opts to a function, the user's opts are mutated. This becomes a problem when a user supplies an opt that is deprecated; e.g. stripe_account instead of stripeAccount. In this scenario:

• Before calling the function:

opts = {
  ...
  stripe_account: ...,  // user supplies a deprecated opt
  ...
}

• After calling the function, the object is mutated:

opts = {
  ...
  stripe_account: ...,
  stripeAccount: ...,  // the function unexpectedly inserts the non-deprecated version of the opt
  ...
}

Because of this mutation, the user is warned that they have supplied both of these args, when in fact they have only supplied one.

This change makes a shallow copy of the user's opts so that this does not happen.

Motivation

fixes #1029

Test plan

• Unit tests

[richardm-stripe]

I'd try to avoid the extra dependency if at all possible. Do you think it is necessary to deep clone? I haven't checked, but my guess would be we aren't doing any mutations more than a single level down and a shallow clone {...opts} would be enough.

[vcheung-stripe]

Using shallow copying with the ... operator, the opts do get mutated, so I think we do need a deep copy. What works is JSON.parse(JSON.stringify(args)), of course this isn't the most robust way of copying. Any thoughts?

[vcheung-stripe]

Actually I may have misread your comment, I will try the shallow copy one level down and report back.

[vcheung-stripe]

Shallow copying one level down works! We do not need this dependency anymore. ptal @richardm-stripe

[richardm-stripe]

LGTM!

[jacoblee93]

Hey @vcheung-stripe and @richardm-stripe, we're using Node 6 this line broke our build -- Node 6 doesn't support the spread operator in objects:

const params = {...args.pop()};

Can we change this to something else? Version deprecations shouldn't be done in a minor release at any rate. I'll open a PR shortly.

[paulasjes-stripe]

Hi @jacoblee93, we ended support for Node 6 as of version 8 of stripe-node: https://github.com/stripe/stripe-node/wiki/Migration-guide-for-v8

I admit that finding that information was harder that it should have been. I'll put up a PR shortly that clearly states our supported versions in the main readme.

[jacoblee93]

Dang. Thanks for letting me know.