Add undefinedReplacement option to diffJson

[ewnd9]

Fixes #155

Please, let me know if I need to change styling / rename undefinedReplacement to something more concise / anything else.

[ewnd9]

I had to assign undefinedReplacement directly to jsonDiff because this.options is overriden each time at the base#diff method (https://github.com/kpdecker/jsdiff/blob/master/src/diff/base.js#L10).

[kpdecker]

Humm. This is not ideal as it causes side effects in the global space. Did you try to pass options through?

[ewnd9]

I had to add this to keep coverage at 100% which was dropped due to the code below

if (typeof options === 'function') {
  callback = options;
  options = {};
}

[kpdecker]

Humm. This is not ideal as it causes side effects in the global space. Did you try to pass options through?

[ewnd9]

My apologies for distraction, it's indeed working with just options.

If I recall correctly, I was trying to keep signature of jsonDiff.diff(oldObj, newObj, callback) but now I see it is already handled at https://github.com/kpdecker/jsdiff/blob/master/src/diff/base.js#L6-L9

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I've pushed a new commit with changes

[ewnd9]

@kpdecker Could you release a new version on npm, please?

[kpdecker]

Released in 3.2.0