{"op":"add"} has no value if the value is undefined.

[wolfgang42]

RFC 6902, section 4.1 ("add") says: "The operation object MUST contain a "value" member whose content specifies the value to be added."

jsonpatch.compare() can, however, produce an add operation with no value when the value is undefined.

Test case:

original = {foo: 1};
changed = {foo: 1, bar: undefined};
patch = jsonpatch.compare(original, changed);
jsonpatch.apply(original, patch);

Result: Error: 'value' MUST be defined

[warpech]

Please note that undefined is not a valid value in JSON (ECMA-404).

Theoretically we could ditch checking via undefined for hasOwnProperty, but that would have performance implications: http://jsperf.com/hasownproperty-vs-undefined so I prefer to stick to the standard

[warpech]

I think that actually the right solution is that jsonpatch.compare should create:

["op": "remove", "path": "/bar"]

WDYT?

[warpech]

Related: #32

[sonnyp]

See #32 (comment)

[wolfgang42]

Indeed, this is a duplicate of #36; I missed this because I was looking specifically for {"op": "add"}. Personally, I think that it should not be possible for fast-json-patch to emit an invalid json-patch; in this case, it ought to raise an error informing the programmer that undefined is invalid JSON instead.

[sonnyp]

@wolfgang42 👍

[tomalec]

I've just added few test cases for it, so it should no longer result in error. Behavior in case of undefined is described at README.md, and at #32

[miyconst]

The test cases added by @tomalec does not work without native Object.observe support.
As stated in the issue #82, the Object.observe is no longer supported, so we can't rely on it.

Current implementation of dirty checking creates mirror of object with the following code:

mirror.value = JSON.parse(JSON.stringify(obj));

As mentioned above, undefined is not a valid JSON value, and JSON.stringify ignores such properties.

This leads to:

• Replacing value of an undefined property generates add patch instead of replace.
• Removing property with undefined value does not generate any patches.

[warpech]

Fixed in 1.0.0