Is using Immutable.set() with "deep" parameters in ImmutableJS safe?

Question

Trying out immutable-js, I found something that I don't fully understand and want to make sure I'm using set correctly.

Basically, if you use "set()" to set a value of a property with an object or array, it stores a raw object/array, whereas if you use merge, it does what I'd expect, converting the raw array to an immutable list.

So my question is: Should you avoid using set() with objects/arrays for parameter 2?

Jasmine Test example here:

it("can do a thing you shouldn't do(?) - inject a normal object into a Map via set", function(){
    const expected = fromJS({ a:  [ 3, 4, 5 ] });
    const set_value = expected.set("a", [3, 4,5]);
    const merge_value = expected.merge({"a": [3, 4,5]});
    expect(expected.get("a")).toEqualImmutable(set_value.get("a")); // Fails
    expect(expected.get("a")).toEqualImmutable(merge_value.get("a")); // Passes
})

Output is:

Message:               
  Expected             
  List [ 3, 4, 5 ]     
   to equal            
  3,4,5

Simon Baumgardt-Wellander · Accepted Answer · 2018-01-12 18:03:16Z

2

You should use set() with objects/arrays only when you want your Immutable objects to contain objects/arrays.

That is to say, this is a style choice without a definitive right answer. A good rule of thumb is to not put mutable object into your immutable collections unless you know what you're doing and you have a really good reason to.

Is it safe?

That depends on what you mean by safe. As of 4.0.0-rc8 getIn, setIn, updateIn, merge, toJS, etc. should all work with Immutable collections containing mutable data, so you're safe in that regard.

On the other hand, if you start putting mutable values in your immutable containers, you lose a lot of the benefits of having an immutable collection in the first place. You no longer have the guarantee that a reference to the same object will always contain the same data.

answered Jan 12, 2018 at 18:03

Simon Baumgardt-Wellander

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