Can deepmerge-ts merge circular object?

[fatihaziz]

adding a test like this

test(`can merge circular object`, t => {
  const x = {
    a: { b: { c: `value1`, e: `im x`} },
  } as any
  x.a.b.a = x.a 
  x.a.b.b = x.a 

  const y = {
    a: { b: { c: `value2`, d: `val2` } },
    b: { b: { c: `value2`, d: `im y` } },
  } as any
  y.b.b.b = y.b 
  y.b.b.c = y.b 

  const expected = {
    a: {
      b: {
        a: x.a,
        b: x.a,
        c: `value2`,
        d: `val2`,
        e: `im x`,
      },
    },
    b: {
      b: {
        b: y.b,
        c: y.b,
        d: `im y`,
      },
    },
  }

  const merged = deepmerge(x, y)

  t.deepEqual(merged, expected)
  t.true(merged.a.b.a === merged.a)
  t.true(merged.a.b.b === merged.a)
})

there is some reason I cant test it myself on my desktop.

[RebeccaStevens]

Yes, it will work.

However, note that merged.a.b.a will point to the original x.a object, not merged.a. If you want it to point to the new merged.a object, you'll need to customize the merging using deepmergeCustom.

[fatihaziz]

ohhhh, i see.
so

  t.true(merged.a.b.a === merged.a)
  t.true(merged.a.b.b === merged.a)

will fails?

[fatihaziz]

would you give the sample code using deepmergeCustom you mentioned above?

[RebeccaStevens]

ohhhh, i see. so

  t.true(merged.a.b.a === merged.a)
  t.true(merged.a.b.b === merged.a)

will fails?

Yes, I believe so.

[RebeccaStevens]

would you give the sample code using deepmergeCustom you mentioned above?

I had a quick look into this and it seems that I might need to expose more meta data to make this possible.

Here's a quick start I made. I don't have time to work on it more right now but I should hopefully be able to look into it tomorrow. Feel free to see if you can get it working in the mean time.

const mergeSettings: DeepMergeOptions<{
  seen: WeakMap<object, object>
}> = {
  metaDataUpdater: (meta = { seen: new WeakMap() }, metaMeta) => {
    // update seen

    return { ...meta };
  },
  mergeOthers: (values, utils, meta) => {
    if (!meta) {
      return utils.actions.defaultMerge;
    }

    // check if seen and re-reference.
  }
};

[fatihaziz]

I create a sandbox here https://stackblitz.com/edit/typescript-odnbzv?file=index.ts

and its working as we expect