OK in this case it looks like it is doing a lot of at runtime checking of arguments to treat them differently, based on what type of argument they are. If we restrict use to only work with arrays, or whatever we have in our project, where we need `difference`, then it should become much simpler and an easy rewrite. An alternative could be to have another argument, that is the function that gives us the `next` thing. Then the logic for that is to be specified by the caller.
Tree shaking however, will not help you, if you have to first install a library using NPM. It will only help you reduce overhead in the code served to a browser. Malicious code can run much earlier, and would be avoided, if you rewrite or extract relevant code from a library, avoiding to install the library using NPM. Or is there some pre-installation tree shaking, that I am unaware of? That would actually be interesting.
https://github.com/lodash/lodash/blob/main/dist/lodash.js#L7...
So you also need to copy isArrayLikeObject, baseDifference and baseFlatten.
For baseDifference, you also need to copy arrayMap and baseUnary.
For baseFlatten, you also need to copy arrayPush.
For isArrayLikeObject, you also need to copy isArrayLike and isObjectLike.
For isArrayLike, you also need to copy isLength and isFunction.
For isFunction, you also need to copy isObject and baseGetTag.
For baseGetTag, you also need to copy getRawTag and objectToString.
I don’t have time to dig any deeper, just use tree-shaking ffs.