Calculating the average without knowing all previous values

addAverageData.js

var data = {};

addAverageData(data, 'averageAppleDiameter', 5);
addAverageData(data, 'averageAppleDiameter', 7);
addAverageData(data, 'averageAppleDiameter', 8);
addAverageData(data, 'averageAppleDiameter', 9);

addAverageData(data, 'averagePearDiameter', 9);
addAverageData(data, 'averagePearDiameter', 4);
addAverageData(data, 'averagePearDiameter', 6);
addAverageData(data, 'averagePearDiameter', 8);

function addAverageData(data, key, value) {
    if (data[key]) {
        data[key].value = addFraction(value, data[key].value, data[key].samples);
        data[key].samples += 1;
    } else {
        data[key] = {};
        data[key].value = value;
        data[key].samples = 1;
    }
}

function addFraction(currentValue, addValue, addValueIndex){
	var indexFromOne = addValueIndex + 1;
	var fraction = 1 / indexFromOne;
	var fractionCurrent = (indexFromOne - 1) / indexFromOne;
	currentValue = currentValue*fractionCurrent + addValue*fraction;
	return currentValue;
}

averageFractions.js

function addFraction(currentValue, addValue, addValueIndex){
	var indexFromOne = addValueIndex + 1;
	var fraction = 1 / indexFromOne;
	var fractionCurrent = (indexFromOne - 1) / indexFromOne;
	currentValue = currentValue*fractionCurrent + addValue*fraction;
	return currentValue;
}

var values = [0.003,5,3,2,7.323, 5.6, 8.669234, 456.45];

var total = 0;
for (var i = 0; i < values.length; i++) {
	total += values[i];
};
console.log('classical: '  + total/values.length);

var total = 0;
for (var i = 0; i < values.length; i++) {
	total = addFraction(total, values[i], i);
}

console.log(total);