Allow the source object to be null or undefined

[monolithed]

➜ node
> let deepmerge = require('deepmerge');
undefined
> deepmerge({}, undefined)
TypeError: Cannot convert undefined or null to object

Could you provide the same behaviour like Object.assign?

[TehShrike]

It's important to realize that deepmerge isn't compatible with Object.assign in several important ways - the first way being the obvious one, where Object.assign isn't recursive, and the second way being that Object.assign returns the first argument that you pass, while deepmerge creates a new target object, and returns that.

You may want to look into deep-assign.

That said, I would be open to returning a clone of the first argument when the second argument is null or undefined. I think it would just take wrapping this block with an if (source != null).

Unless anyone else has any thoughts, I'll say a pull request with tests would be welcome.

[monolithed]

You may want to look into deep-assign.

Nope, they are so different:

➜ node
> var merge = require('deep-assign')

> merge([1, 2], [2, 3])
[ 2, 3 ]

> merge({a: 1}, {a: [2]})
{ a: { [Number: 1] '0': 2 } }

➜ node
> var merge = require('deepmerge')

> merge([1, 2], [2, 3])
[ 1, 2, 3 ]

> merge({a: 1}, {a: [2]})
{ a: [ 2 ] }

[TehShrike]

It's true - deep-assign has optimal compatibility with Object.assign, in that all it does is implement recursion on top of Object.assign. deepmerge opts for merging children with custom logic.

[TehShrike]

If nobody is motivated to open pull requests with tests or implementation, I'll close this eventually.

[TehShrike]

Should undefined (or maybe even null) be treated like an empty object when passed to the merge function?

If so, should that be the case when it's passed in to the target, or just the source?

See #80

[macdja38]

typeof null is an object... so it would probably make sense to treat it like {}. Not sure if we should do the same with undefined though.

[TehShrike]

If this library mutates objects by changing its properties (which is what it has done), then I don't like the idea of treating null or undefined as special "empty object" values.

But if this library is moving to an "always clone onto a new object no matter what" paradigm (like I'm pushing it to), it's more understandable.

[TehShrike]

I still feel really nervous about adding magical defaults :-x

Cloning is a non-trivial thing to have a mental model for (as you can see by looking back over all the issues and pull requests on this repository), I don't want to try to guess at what people will expect here.

[danmarshall]

My workaround for this is to use the .all method which takes an array, then use Array.filter(Boolean) to get rid of falsey stuff like undefined:

deepmerge.all([{foo:"foo"}, undefined].filter(Boolean))

[TehShrike]

This path has too many scary implications for me. I'm going to close this.

[OmgImAlexis]

For those really needing this I use this as a work around.

const deepmerge = require('deepmerge');
const merge = (first, second) => deepmerge({ object: first }, { object: second }).object;
merge({ }, undefined); // undefined