如何访问 JavaScript 中 function 中的变量？

Question

I'm almost finishing my first project with React Native which is an expenditure app.

I'm building a chart from all my expenses in 2 currencies, the code is working I just have a small problem with accessing a local variable.

I would like to access the 2 sum variable inside this function, so I can use it in my return for React Native to build a chart.

  // Get $ currency From fire base
  const q = query(collection(db, "users"),where("selected", "==", "Gasto"), where("moneda", "==", "$"));
  const unsubscribe = onSnapshot(q,(querySnapshot) => {
    const dolarCurrency = [];
    const months =[];
    querySnapshot.forEach((doc) =>{
      dolarCurrency.push(doc.data().cantidad);
      months.push(doc.data().fecha)
    })
    const hash = months.map((Day) => ({ Day }));
    const hashDolar = dolarCurrency.map(( Amount ) => ({ Amount }))

    const output = hash.map(({Day},i) => ({Day, ...hashDolar[i]}));
    
    /// I need this variable below
    const sum = output.reduce((acc, cur)=> {
      const found = acc.find(val => val.Day === cur.Day)
      if(found){
          found.Amount+=Number(cur.Amount)
      }
      else{
          acc.push({...cur, Amount: Number(cur.Amount)})
      }
      return acc
    }, [])
    })

  // Get C$ currency from Firebase
  const q2 = query(collection(db, "users"), where("selected", "==", "Gasto"),where("moneda", "==", "C$"));
  const unsubscribe2 = onSnapshot(q2, (querySnapshot) =>{
    const localCurrency = [];
    const months2 = [];
  querySnapshot.forEach((doc) => {
    localCurrency.push(doc.data().cantidad)
    months2.push(doc.data().fecha)
    })
  const hash = months2.map((Day) => ({ Day }));
  const hashLocalCurrency = localCurrency.map(( Amount ) => ({ Amount }))

  const output = hash.map(({Day},i) => ({Day, ...hashLocalCurrency[i]}));

  /// I need this variable below
  const sum = output.reduce((acc, cur)=> {
    const found = acc.find(val => val.Day === cur.Day)
    if(found){
        found.Amount+=Number(cur.Amount)
    }
    else{
        acc.push({...cur, Amount: Number(cur.Amount)})
    }
    return acc
  }, [])
  })

Any help or advice is welcome and appreciated!

Answer 1

You can either try state or ref, depends on whether UI part is to be updated, if UI is to be updated then state else ref does the job

const [sum,setSum] = useState(0) or

const sumRef = useRef(0)

Then after that

 const sum = output.reduce((acc, cur)=> {
    const found = acc.find(val => val.Day === cur.Day)
    if(found){
        found.Amount+=Number(cur.Amount)
    }
    else{
        acc.push({...cur, Amount: Number(cur.Amount)})
    }
    return acc
  }, [])
  })

You can either setSum(sum) or sumRef.current = sum

Hope it helps, feel free for doubts