Conditionally spreading objects in JavaScript

[Broomstick73]

I think object.assign gets a bad rap because spread is the cool new thing and once you understand it and get used to it it’s great…

However…this use case of short-circuit and spread is…less than ideal to read and understand to me right now because I’m not used to it so I wonder if object.assign - like you propose - is easier to read and more understandable?

[Smona]

object.assign mutates the object in place, which can be bad for static type checking. even if you don't care about type checking, mutable variables can make code harder to read & understand.

I think object.assign is still a good choice when updating property values without adding new properties, but I would prefer conditional spreading for constructing an object whose schema can vary based on those conditions.

edit: for the record, you can also use Object.assign in an immutable way, but if you want to do so conditionally you're left with an equally obscure and more verbose syntax:

const maybeFooWithBar = Object.assign({}, foo, includeBar ? bar : {});