Push to array with AsyncStorage

Question

I'm trying to build a favourite system with AsyncStorage in React Native. On my ProductDetailScreen I have the corresponding ProdID available. I'd like to save the ProdID to AsyncStorage.

  const arr = [];
  const saveFavorites = async () => {
    arr.push(ProdID);
    await AsyncStorage.setItem("FAVORITES", JSON.stringify(arr));
  };

  const getFavorites = async () => {
    const favs = await AsyncStorage.getItem("FAVORITES");
    let parsedFavs = JSON.parse(favs);
    console.log(parsedFavs);
  };

This works. However if I go to the next Product and click the saveFavorites button, obviously the arr gets initiated with an empty array.

I can't wrap my head around how I would create the empty array if the saveFavorites button was never clicked before but push to the array if there is already an ID in it. I tried it with useState and useEffect but without success. Any help would be appreciated.

Gaurav Roy · Accepted Answer · 2020-01-26 10:45:01Z

1

You can do like

const saveFavorites = async () => {
 let data = await AsyncStorage.getItem("FAVORITES");

let arr = JSON.parse(data);
    arr.push(ProdID);
    await AsyncStorage.setItem("FAVORITES", JSON.stringify(arr));
  };

try with this

answered Jan 26, 2020 at 10:45

Gaurav Roy

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4 Comments

hapfr Over a year ago

Ok, still a little problem. If there array is completely empty at the beginning, I get this error [Unhandled promise rejection: TypeError: null is not an object (evaluating 'arr.push')]

Gaurav Roy Over a year ago

you can do something like arr ? arr.push(ProdID): [];

Gaurav Roy Over a year ago

hope it helps , feel free for doubts

hapfr Over a year ago

Thanks. It only works if I do it like this: arr ? arr.push(ProdId) : (arr = [ProdId]); Only problem left ist, to check if ProdId is already in arr so that it does not get pushed into the array.

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