Getting errors while trying some condition on an array

Question

Trying to check if an array has some values and display it once in typescript

const items = products?.reduce((prev: any, current) => {
  if (!current?.data()?.drinkName in prev) {
    prev[current?.data()?.category] = [];
  }
   prev[current?.data()?.category].push(current?.data()?.category);
   return prev;
}, {});

Error:

The left-hand side of an 'in' expression must be a private identifier or of type 'any', 'string', 'number', or 'symbol'.

Niv Kor · Accepted Answer · 2022-03-11 13:20:45Z

2

You accidentally converted current?.data()?.drinkName to a boolean by adding ! before it. Try wrapping the whole statement with parenthesis like so !(current?.data()?.drinkName in prev). This way the ! negates the whole statement and not just the left part.

I would have also added a condition that checks whether current?.data()?.drinkName is null before checking if it exists in prev, because theoretically prev might contain null.

if (!(current?.data()?.drinkName) || !(current?.data()?.drinkName in prev))

answered Mar 11, 2022 at 13:20

Niv Kor

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