Handling "undefined"

[snicol21]

Maybe this is by design, but I was surprised to learn that this:

import { merge } from "merge-anything"

const defaultTheme = {}
const theme = undefined

merge(defaultTheme, theme)

Returns undefined. Is this expected, maybe it is, but I was kind of expecting it to return {}. Am I right?

I would hate to have to handle this scenario like this everytime:

merge(defaultTheme, theme || {})

[mesqueeb]

@snicol21 It's by design 😅
i'm able to change it with a major version if you want.
When using merge to change props inside an object, you would probably want to keep the current implementation I imagine though. But Ach, I guess it's always case-by-case 🤷🏻‍♂️

[snicol21]

@snicol21 It's by design 😅

i'm able to change it with a major version if you want.

When using merge to change props inside an object, you would probably want to keep the current implementation I imagine though. But Ach, I guess it's always case-by-case 🤷🏻‍♂️

Thanks for responding @mesqueeb, this is the wrapper I ended up creating to accommodate this use case.

import { merge as mergeAnything } from "merge-anything"

// Replaces 'null' or 'undefined' values with an empty object in a tuple,
// ensuring that all elements are valid objects for merging.
type Defined<T> = {
  [K in keyof T]: Exclude<T[K], null | undefined>
}

// Recursively merges a tuple of objects or null/undefined values,
// filtering out the null/undefined to prevent type errors during merge.
type MergeDefined<T> = T extends [infer First, ...infer Rest]
  ? First extends object
    ? Rest extends (object | undefined | null)[]
      ? First & MergeDefined<Rest>
      : never
    : never
  : unknown

// A merge function that combines multiple objects, including those
// that may be 'null' or 'undefined', into a single object with proper types.
export function merge<T extends (object | undefined | null)[]>(...objects: T): MergeDefined<T> {
  // Create an array of objects, converting 'null' or 'undefined' values to empty objects.
  const safeObjects = objects.map((obj) => (obj == null ? {} : obj)) as Defined<T>
  // Merge the objects into one, casting the result to the recursive merge type.
  return mergeAnything({}, ...safeObjects) as MergeDefined<T>
}

[quantizor]

Related to this, if you try to apply a partial of the first type it causes problems because the resulting type gains | undefined for all the partial fields where the point of it is just to selectively override fields, e.g.

const baseTokens: ColorTokensWithModes = {
  uiBg: 'white',
  uiBgAlternate: 'lightgray',
}

const tokens: ColorTokensWithModes = merge<ColorTokensWithModes, DeepPartial<ColorTokensWithModes>[]>(baseTokens, {
  uiBg: colors.white,
});