Lodash merge including undefined values

问题

I'm trying to use Lodash to merge object A into object B, but the trouble I am having is that object A has some undefined values and I want these to be copied over to object B.

Lodash docs for _.merge() says:

"Recursively merges own enumerable properties of the source object(s), that don't resolve to undefined into the destination object."

Is there another function that can do this, or can it be easily overwritten?

EDIT A:

Sample input:

A = {
  name: "Bob Smith",
  job: "Racing Driver",
  address: undefined
}

B = {
  name: "Bob Smith",
  job: "Web Developer",
  address: "1 Regent Street, London",
  phone: "0800 800 80"
}

Expected Output

B = {
  name: "Bob Smith",
  job: "Racing Driver",
  address: undefined,
  phone: "0800 800 80"
}

EDIT B:

Just to confirm, it needs to be a "deep" merge. object may contain nested objects.

回答1:

Easiest would be to use 3rd package for this https://github.com/unclechu/node-deep-extend which goal is only deep merging and nothing else.

回答2:

_.assign/_.extend will do that:

_.assign(B, A);

回答3:

Check this out. It is a small gist containing a deep extend lodash method which you can use within your own application. This will also allow you to get the functionality you need without adding another dependency in your app (since you're already using lodash)

回答4:

Thanks to @Bergi - https://stackoverflow.com/a/22581862/1828637 - assign will keep undefined. I did a customizer here using assignWith for deep merge with customizer, as i use this in redux/react:

function keepUnchangedRefsOnly(objValue, srcValue) {
    if (objValue === undefined) { // do i need this?
        return srcValue;
    } else if (isPlainObject(objValue)) {
        return assignWith({}, objValue, srcValue, keepUnchangedRefsOnly);
    } else if (Array.isArray(objValue)) {
        if (isEmpty(objValue) && !isEmpty(srcValue))return [...srcValue];
        else if (!isEmpty(objValue) && isEmpty(srcValue)) return objValue;
        else if (isEmpty(objValue) && isEmpty(srcValue)) return objValue; // both empty
        else return [ ...objValue, ...srcValue ];
    }
}

Usage like this - https://stackoverflow.com/a/49437903/1828637

来源：https://stackoverflow.com/questions/22581220/lodash-merge-including-undefined-values

标签

javascript

lodash