Typescript react, how to set state of an array

Question

I am currently facing an issue where I am getting data from my API, and then I would like to manipulate the data to create an array called events which I can use to pass to my calendar. I am trying the following:

const createEvents = () => {
        workouts.map((w)=> {
            setEvents(...events, 
            {           
                id: w.id,
                title: w.name,
                date: w.dateOfWorkout
            });

        });

However I am getting the error where it states that it was expecting only 1 argument, but got 2 instead. Whilst googling, I came across this website (https://daveceddia.com/usestate-hook-examples/) which had an example very similar to the above. I define my events as follows:

const [events, setEvents] = useState([]);

What am I missing here? I am fairly new to react and TS/JS. I come from C# where in essence I am trying to do the equivalent of:

myData.Select(x => new {
Id = x.Id,
...
})

I see, that makes sense. I was hoping though that by using the spread operator it would add the data to the array as is displayed in the url i linked — SomeStudent
– SomeStudent, Commented May 8, 2020 at 0:19
Well spread does work that way, I was just pointing out that not returning from the map callback is a common error in JavaScript. — Aluan Haddad
– Aluan Haddad, Commented May 8, 2020 at 0:22
Gotcha, thank you very much. I will make sure to keep it in mind — SomeStudent
– SomeStudent, Commented May 8, 2020 at 0:23

monsty · Accepted Answer · 2020-05-08 00:26:06Z

2

You can try to put your arguments into an array ?

setEvents([
//--------^
  ...events, 
  {           
    id: w.id,
    title: w.name,
    date: w.dateOfWorkout
  }
]);

Btw, even if it's working, I won't call setEvents inside a map (or inside any other loop), that should not be used that way.

I would probably do something like that :

const createEvents = () => {
  setEvents([...events,
    workouts.map((w) => ({
      id: w.id,
      title: w.name,
      date: w.dateOfWorkout
    }))
  ]);
};

edited May 8, 2020 at 0:26

answered May 8, 2020 at 0:20

monsty

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2 Comments

SomeStudent Over a year ago

this does remove the error, atm it seems though my mobx is not setting my observable correctly. I do get the data from my api successfully. Time to debug that, but the above code does fix the issue of compiling.

SomeStudent Over a year ago

Thank you very much, using your method I was able to figure out the missing pieces)

Maximiliano Poggio · Accepted Answer · 2020-05-08 00:21:34Z

1

try this:

const newEvents = 
        workouts.map((w)=> ({
                ...events,
                id: w.id,
                title: w.name,
                date: w.dateOfWorkout
            })
        )

then, you can call:

setEvents(newEvents)

In your example, you are not returning nothing in map. Map is a higher order function, it just receives a function as parameter and returns a converted array of objects.

answered May 8, 2020 at 0:21

Maximiliano Poggio

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Comments

SomeStudent · Accepted Answer · 2020-05-08 00:53:19Z

Not so much as an answer, but rather a thank you those who responded. Using your answers, along with reading some more about react/mobx. I realized that what I needed to do in order to fulfil my goal was to create a computed property in my WorkoutStore.ts as follows:

@computed get events() { const data = this.workouts.map((w) => ({ id: w.id, title: w.name, date: w.dateOfWorkout }))

    return data;
};

and then I can do the following in my Workout.tsx file:

const {getWorkouts, events} = root.workoutStore;

    useEffect(() => {
        console.log("In here");
        if(match.params.id) {
            getWorkouts(match.params.id);
        }
    }, [match.params.id, getWorkouts])

After it is mounted, I can now easily just do events={events} inside of my full calendar component. The reason for shifting it over to the store is that otherwise (I assume due to order of operations and the like), the workout object was always empty and thus no events were computed off of it.

Thank you once again to Max, and monsty for steering me to the right direction

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