how to add new array with old array useing useState js?

Question

i want to make all arrays in one array during a loop , example :

i have array of objects

[{1 ,2,3},{4,5,6}]

used function to convert each object to array [1 ,2,3] [4,5,6]

how i can merge both of this array to be one array [1,2,3,4,5,6]

and this is my code


  const [start, setStart] = useState<Date[]>([]);


  useEffect(() => {
    publicHoliday?.map((holiday) => {
      const eventStartDate = holiday.startDate;
      const eventEndDate = holiday.endDate;

      const holidayDates = enumerateDaysBetweenDates(eventStartDate, eventEndDate);

     //holidayDates is array 


//give me error here "  Type 'Date | Date[]' is not assignable to type 'Date'.
  Type 'Date[]' is missing the following properties from type 'Date': toDateString, toTimeString, toLocaleDateString, toLocaleTimeString, and 37 more.ts(2322)"

      setStart([...start, holidayDates]);
      return;
    });
  }, [publicHoliday]);

[{1 ,2,3},{4,5,6}] is not an array.

Spectric
– Spectric

2021-08-25 18:56:46 +00:00
Commented Aug 25, 2021 at 18:56 — Spectric
– Spectric, Commented Aug 25, 2021 at 18:56

Chuck · Accepted Answer · 2021-08-25 19:04:06Z

3

Try this one.

 useEffect(() => {
     updatedData = []
     publicHoliday?.forEach((holiday) => {
        ...
        updatedData = [...updatedData, ...holidayDates]
        ...
     })
     setStart(updatedData)
     ...

This is the simplified the merge logic.

var updated = []
// origin = [[1,2,3], [4,5,6]]
origin.forEach( (item, index) => updated = [...updated, ...item]) 
// updated = [1,2,3,4,5,6]

answered Aug 25, 2021 at 19:04

Chuck

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2 Comments

Ammar ALSananni Over a year ago

thanks , working but the now start array like this [ Array,Array,Array] , how to make it one array

Chuck Over a year ago

origin.forEach( (item, index) => updated = [...updated, ...item]) Here origin is [Array, Array...], and updated is the result you are looking for.

Emmanuel Ponnudurai · Accepted Answer · 2021-08-25 19:17:17Z

0

It appears that this function enumerateDaysBetweenDates is returning Date | Date[] which is what the error eventually tells.

You should first see if you can adjust that method to always return Date[] so that its clear.

If you can't, then you must verify on the calling side, if it's an array or not and proceed accordingly,

if(Array.isArray(holidayDates)){
  setStart([...start, ...holidayDates]);
}
else{
  setStart([...start, holidayDates]);
}

answered Aug 25, 2021 at 19:17

Emmanuel Ponnudurai

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