Using for arrays? deleted seems to be wrong

[giorgio79]

Tried using it for arrays, but it seems deleted items are tackled incorrectly. The script is not taking the shortest path.

eg https://runkit.com/giorgio79/5bead0643e02a00012ed51d0

const { diff, addedDiff, deletedDiff, detailedDiff, updatedDiff } = require("deep-object-diff");

const wrong = [
 "Tom",
 ",",
 "was",
 "involved",
 "in"
];

const right = [
 "Tom",
 "was",
 "involved",
 "in"
 ];

console.log(detailedDiff(wrong, right));

getting

Object
added: Object {}
deleted: Object {4: undefined}
updated: Object {1: "was", 2: "involved", 3: "in"}

I would have expected
Object
added: Object {}
deleted: Object {1: ","}
updated: Object {}

[drdreo]

You are right. Even the documentation example can't distinguish deletes on the same property.

This behavior is actually quiet reasonable. How would you distinguish between an update and a delete? Maybe this is even the desired behavior in some cases (queue data structure).

const lhs = {
  foo: {
    bar: {
      a: ['a', 'b','c'],
      b: 2,
      c: ['x', 'y'],
      e: 100 // deleted
    }
  },
  buzz: 'world'
};

const rhs = {
  foo: {
    bar: {
      a: ['a', 'c'], // index 1 ('b')  deleted
      b: 2, // unchanged
      c: ['x', 'y', 'z'], // 'z' added
      d: 'Hello, world!' // added
    }
  },
  buzz: 'fizz' // updated
};

console.log(detailedDiff(lhs, rhs));

// produces: foo.bar.a.1: 'c' -->  updated
// foo.bar.a.2: undefined -->  deleted

[devniel]

got the same problem. is it a bug, right ?

[anko]

I think this is and should continue to be the intended behaviour.

Reasoning, following @giorgio79's example:

The operation to get from

[ "Tom", ",", "was", "involved", "in" ]

to

[ "Tom", "was", "involved", "in" ]

is to shift everything else up 1 index to cover over the ",".

That matches what the diff you see is telling you:

added: Object {}
deleted: Object {4: undefined} // delete last
updated: Object {1: "was", 2: "involved", 3: "in"} // shift everything up

If it said this,

added: Object {}
deleted: Object {1: ","}
updated: Object {}

that would imply the array should be transformed to

[ "Tom", undefined, "was", "involved", "in" ]

which is a different array!

[r3wt]

anko is correct, this is intended behavior.

[mattphillips]

Gonna close this as it is the correct behaviour as @anko explains above.

Thanks @anko for taking the time to add a clear explanation 😄