Hacker News Reader

Comment by bovermyer | Hacker News Reader

This is great. However, it gives the example of copying a variable by assigning another variable to it. This doesn't copy a variable's contents - it makes the new variable a pointer to the original variable.

As someone who doesn't use Javascript much... is there a way to force it to copy the current state of the original variable to the new variable, without it being a reference and without having to use something like lodash?

View on HN

You will need to clone the object somehow. The simplest solution is to go through each of the object properties and create a new object with those same properties (_.clone). Alternatively, recursively go through each property in the object and then keep going deeper through each property that is an object until you get a copy of everything to assign to a new object (_.deepClone)

I think the only reasonable thing that js can do here is what it does - copy the reference. Also, there is a simple way to copy all properties from a object: const copy = { ...object }; Of course, if these properties are themselves objects, then changes in one of them will appear in the other.

One way to have a deep copy which shares nothing is const copy = JSON.parse(JSON.stringify(object)); but that may not always work. In short, copying a arbitrarily large object will probably waste memory, so it should be a little hard so you don't do it unless it's really necessary.

In addition to the cloning stuff, I've seen use of an immutables library [0] to make this stuff a little more explicit and simple. Not sure if that's still fashionable though.

[0] e.g. https://immutable-js.github.io/immutable-js/

The cheaty way is `let copy = JSON.parse(JSON.stringify(val))`. Doesn't work for functions or cyclic structures though.

Reply on news.ycombinator.com