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JavaScript JavaScript Array Iteration Methods Combining Array Methods Combining filter() and reduce()

yoav green
yoav green
8,611 Points
Posted by yoav green
yoav green
8,611 Points

why do we need to "return item" in order to get { name: 'paper towels', price: 6.99 } eventually 

const products = [
  { name: 'hard drive', price: 59.99 },
  { name: 'lighbulbs', price: 2.59 },
  { name: 'paper towels', price: 6.99 },
  { name: 'flatscreen monitor', price: 159.99 },
  { name: 'cable ties', price: 19.99 },
  { name: 'ballpoint pens', price: 4.49 }
];

const newArray = products
  .filter(item => item.price < 10)
  .reduce((highest, item) => {
    if (highest.price > item.price) {
    return highest
    }
    return item
    },)


console.log(newArray);

1 Answer

Dave StSomeWhere
Dave StSomeWhere
19,870 Points
Dave StSomeWhere
Dave StSomeWhere
19,870 Points

If you review the MDN Doc you notice that it says:

accumulator The accumulator accumulates the callback's return values; it is the accumulated value previously returned in the last invocation of the callback, or initialValue, if supplied (see below).

So as the callback function loops through the array, when the next array item (the "item" in return item) is a higher value - return that value and reset the accumulator.

This should be clearer if you add some logging.

Like this:

const products = [
    {name: 'hard drive', price: 59.99},
    {name: 'lighbulbs', price: 2.59},
    {name: 'paper towels', price: 6.99},
    {name: 'flatscreen monitor', price: 159.99},
    {name: 'cable ties', price: 19.99},
    {name: 'ballpoint pens', price: 4.49}
];

const newArray = products
    .filter(item => item.price < 10)
    .reduce((highest, item) => {
        console.log('Highest is --> ' + highest.price);
        console.log('item is --> ' + item.price);
        if (highest.price > item.price) {
            console.log('about to return highest price --> ' + highest.price);
            return highest
        }
        console.log('about to return item --> ' + item.price);
        return item
    },);


console.log(newArray);

// output
Highest is --> 2.59
item is --> 6.99
about to return item --> 6.99
Highest is --> 6.99
item is --> 4.49
about to return highest price --> 6.99
{ name: 'paper towels', price: 6.99 }

Does that clear things up? :tropical_drink: :palm_tree:

yoav green
yoav green
8,611 Points
yoav green
yoav green
8,611 Points

yes, thanks a lot :)