Reacting to reactive variables outside a component

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Hi!

I would like to use reactive vars to handle my global local state in my app. One thing I can’t seem to figure out is how to react to a variable change when I’m outside of a component. Basically I want to do simple stuff like: When this value is updated, run that function to save the new value to a localStorage. I wan tthis reaction to be handled outside of the component because I don’t want it to be linked to a specific component. Whenever this var gets updated from anywhere in the app, I want to react to the change and do some stuff.

I tried putting the stuff I want to run in

typePolicies: {
    Query: {
      fields: {
        something: {
          merge: (_, incoming) => {
            // Run some custom function
            return incoming
          },
        },
      },
    },
  },

and then updateing the reactive var using somethingVar(newValue), but it doesn’t feel like the correct thing to do and the ‘merged’ is not getting called anyway.

Thanks!