Create an array using item from different array

Question

I need to create a new array of objects with 12 item (months & value) on it but it must check if the month exist on other array. If it exist it will push onto the array if not it will have a value of 0

Array to check with

arr1 = 
[
 {
   date: 2024-02,
   value: "100" 
 },
 {
   date: 2024-08,
   person: "200" 
 },
]

What I did

 const getMonthlyAmount = () => {
    let arr = [];

    for (i = 1; i <= 12; i++) {
      arr1.map((item) => {
        if (arr1.date.slice(0, 5) === i) {
          arr.push(item);
        }
      });
    }
    return arr;
  };

Result I want:

arr = [
 {
   date: 2024-01,
   value: 0
 }, 

 {
   date: 2024-02,
   value: "100" 
 },

... continue

 {
   date: 2024-08,
   person: "200" 
 },

... continue

 {
   date: 2024-12,
   value: 0 
 },
]

Answer 1

You could do it like this:

const getMonthlyAmount = () => {
  return Array.from({ length: 12 }, (_, i) => {
    const month = (i + 1).toString().padStart(2, '0');
    const date = `2024-${month}`;

    const foundItem = arr1.find((entry) => entry.date === date);
    
    return foundItem ? foundItem : { date, value: 0 };
  });
};

This will create the "missing" month and set the value to 0 if they do not exist in the original array you provided.

Demo

const arr1 = [
  {
    date: "2024-02",
    value: "100"
  },
  {
    date: "2024-08",
    person: "200"
  },
];

const getMonthlyAmount = () => {
  return Array.from({ length: 12 }, (_, i) => {
    const month = (i + 1).toString().padStart(2, '0');
    const date = `2024-${month}`;

    const foundItem = arr1.find((entry) => entry.date === date);
    
    return foundItem ? foundItem : { date, value: 0 };
  });
};

console.log(getMonthlyAmount());