weighted-average - prevent recalculation for new numbers

const arr1 = generateRandomNumbers(20, 5);
const arr2 = generateRandomNumbers(20, 5);
const { result: arr1WeightedAverage, weight: weightArr1WeightedAverage } = calculateWeightedAverage(arr1);
const { result: arr2WeightedAverage, weight: weightArr2WeightedAverage } = calculateWeightedAverage(arr2);

console.log(arr1WeightedAverage, weightArr1WeightedAverage);
console.log(arr2WeightedAverage, weightArr2WeightedAverage);

const temp = 4;

// how to just calculate the new arr1WeightedAverage without pushing temp into arr1 execting the calculateWeightedAverage
// I do not want to do this process:
// arr1.push(4);
// const newArr1WeightedAverage = calculateWeightedAverage(arr1);
// I just want to:
// const newArr1WeightedAverage = calculateNewWeightedAverage(arr1WeightedAverage, temp);
// what should i write inside this function:
function calculateNewWeightedAverage(previousWeightedAverage: number, newNumber: number) {
    // mathematical logic ...
    // note: i want to recaluculate it without the previous weight
    // although i think it is impossible
    // return new weighted average;
}

function calculateWeightedAverage(arr: number[]) {
    let result = 0, weight = 0;

    for (let i = 1; i <= 5; i++) {
        const weighterAverageCount = arr.filter(item => item === i).length;

        if (weighterAverageCount === 0) continue;

        const weightedAverage = (weighterAverageCount * i);

        weight += (i * weighterAverageCount);
        result += weightedAverage;
    }

    return { result: result / arr.length, weight };
}

function generateRandomNumbers(howManyNumber: number, to: number): number[] {
    const arrayFullOfRandomNumbers = [];

    for (let i = 0; i < howManyNumber; i++) {
        const randomNumberBetweenOneAndTo = Math.round(Math.random() * to);

        if (randomNumberBetweenOneAndTo === 0) continue;

        arrayFullOfRandomNumbers.push(randomNumberBetweenOneAndTo);
    }

    return arrayFullOfRandomNumbers;
}