Format data in javascript

Can be done easily using reduce

PS: Please also provide your attempt when you ask questions here. It'll help us help you better. Thanks

var input = [{
    date: "2021-02-09",
    value: 1,
    user: "Internal"
  },
  {
    date: "2021-02-09",
    value: 1,
    user: "External"
  },
  {
    date: "2021-02-12",
    value: 2,
    user: "Internal"
  },
  {
    date: "2021-02-12",
    value: 1,
    user: "External"
  },
  {
    date: "2021-02-14",
    value: 0,
    user: "External"
  },
  {
    date: "2021-02-14",
    value: 2,
    user: "Internal"
  }
];

var output = input.reduce((acc, curr) => {
  var existingIndex = (acc || []).findIndex(
    (entry) => entry.date === curr.date
  );
  if (existingIndex !== -1) {
    // Only update the entry
    acc[existingIndex].value += curr.value;
    acc[existingIndex][curr.user] += curr.value;
  } else {
    // Insert new entry
    acc.push({
      date: curr.date,
      Internal: curr.user === "Internal" ? curr.value : 0,
      External: curr.user === "External" ? curr.value : 0,
      value: curr.value
    });
  }
  return acc;
}, []);

console.log(output)

You can loop over data like this and filter out the dates and the internal external counts based on your calculations in a new array

const sampleData = [{
    "date": "2021-02-09",
    "value": 1,
    "user": "Internal"
  },
  {
    "date": "2021-02-09",
    "value": 1,
    "user": "External"
  },
  {
    "date": "2021-02-12",
    "value": 2,
    "user": "Internal"
  },
  {
    "date": "2021-02-12",
    "value": 1,
    "user": "External"
  },
  {
    "date": "2021-02-14",
    "value": 0,
    "user": "External"
  },
  {
    "date": "2021-02-14",
    "value": 2,
    "user": "Internal"
  }
];

let formattedData = [];

sampleData.forEach(item => {
  const itemIndex = formattedData.findIndex(newItem => newItem.date === item.date);
  const internalCount = item.user === "Internal" ? item.value : 0;
  const externalCount = item.user === "External" ? item.value : 0;
  if (formattedData.length === 0 || itemIndex === -1)
    formattedData.push({
      date: item.date,
      internal: internalCount,
      external: externalCount,
      total: internalCount + externalCount
    });
  else {
    formattedData.splice(itemIndex, 1, {
      date: item.date,
      internal: formattedData[itemIndex].internal + internalCount,
      external: formattedData[itemIndex].external + externalCount,
      total: formattedData[itemIndex].total + internalCount + externalCount
    });
  }
});

console.log(formattedData);