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Merged
merged 9 commits into from
Dec 18, 2023
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Document diffJson() options #332

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Document diffJson() options
cincodenada Oct 25, 2021
efb6185
Tweaks: fix run-on sentences; backtick JSON.stringify; name the JSON.…
ExplodingCabbage Dec 18, 2023
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Add full stop
ExplodingCabbage Dec 18, 2023
19d4e0c
Correct docs about how stringifyReplacer & undefinedReplacement interact
ExplodingCabbage Dec 18, 2023
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Merge commit 'fffd8a7b1c19630a0f8210c4aa1ac2759e8b5f0a' into patch-1
ExplodingCabbage Dec 18, 2023
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ExplodingCabbage Dec 18, 2023
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ExplodingCabbage Dec 18, 2023
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4 changes: 4 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,10 @@ npm install diff --save
* `Diff.diffJson(oldObj, newObj[, options])` - diffs two JSON objects, comparing the fields defined on each. The order of fields, etc does not matter in this comparison.

Returns a list of change objects (See below).

Options
* `stringifyReplacer`: A custom replacer function. Operates similarly to the `replacer` parameter to [`JSON.stringify()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#the_replacer_parameter), but must be a function. `undefined` will _not_ be replaced by this function; see the next option.
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@ExplodingCabbage ExplodingCabbage Dec 18, 2023

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undefined will not be replaced by this function

I don't think this is true. Looking at the code, it seems like the only place that undefinedReplacement gets used is in the default implementation of stringifyReplacer, and that if you provide both, then undefinedReplacement simply gets ignored. There doesn't seem to be any special logic preventing stringifyReplacer from running on an undefined value either:

> diff.diffJson(
...     {x: undefined},
...     {x: "bob"}
... )
[
  { count: 1, added: undefined, removed: true, value: '{}' },
  {
    count: 3,
    added: true,
    removed: undefined,
    value: '{\n  "x": "bob"\n}'
  }
]
> 
> diff.diffJson(
...     {x: undefined},
...     {x: "bob"},
...     {
...         undefinedReplacement: "bob",
...     }
... )
[ { value: '{\n  "x": "bob"\n}', count: 3 } ]
> 
> diff.diffJson(
...     {x: undefined},
...     {x: "bob"},
...     {
...         undefinedReplacement: "jim",
...         stringifyReplacer: (k, v) => k == "x" ? "bob" : v
...     }
... )
[ { value: '{\n  "x": "bob"\n}', count: 3 } ]
> 
> diff.diffJson(
...     {x: undefined},
...     {x: "bob"},
...     {
...         stringifyReplacer: (k, v) => k == "x" ? "bob" : v
...     }
... )
[ { value: '{\n  "x": "bob"\n}', count: 3 } ]

Maybe what you wrote here was true when you opened the PR - dunno, haven't checked - but it's wrong now.

* `undefinedReplacement`: A value to replace `undefined` with. By default it will not be replaced, and replacements for `undefined` from `stringifyReplacer` will not be used.

* `Diff.diffArrays(oldArr, newArr[, options])` - diffs two arrays, comparing each item for strict equality (===).

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