how to use reduce javascript


function flattenArray(data) {
// our initial value this time is a blank array
const initialValue = [];

// call reduce on our data
return data.reduce((total, value) => {
// if the value is an array then recursively call reduce
// if the value is not an array then just concat our value
return total.concat(Array.isArray(value) ? flattenArray(value) : value);
}, initialValue);
}

//note idx and sourceArray are optional
const sum = array.reduce((accumulator, element[, idx[, sourceArray]]) => {
//arbitrary example of why idx might be needed
return accumulator + idx * 2 + element
}, 0);

const sum = array.reduce((accumulator, element) => {
return accumulator + element;
}, 0);
// An example that will loop through an array adding
// each element to an accumulator and returning it
// The 0 at the end initializes accumulator to start at 0
// If array is [2, 4, 6], the returned value in sum
// will be 12 (0 + 2 + 4 + 6)

const product = array.reduce((accumulator, element) => {
return accumulator * element;
}, 1);
// Multiply all elements in array and return the total
// Initialize accumulator to start at 1
// If array is [2, 4, 6], the returned value in product
// will be 48 (1 * 2 * 4 * 6)

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