The reduce
array method is an interesting method because unlike filter
and map
that takes one parameter during it's most basic usage, the reduce
method takes two parameters. The first one is the accumulator and the other is the parameter of the current value that will be worked on.
reduce
allows for items to be summed up or brought together.
Let's see a few examples on it.
Were going to try to sum up the numbers in the following array:
const nums = [1, 2, 3, 4, 5]
Solution
const sumNumbers = nums.reduce((sum, num)=> sum + num, 0)
console.log(sumNumbers)
//output is 15
Here, you will see that apart from num
which is the current value parameter that we will work on according to every number in the array, the sum
which is another parameter and the accumulator taken in by reduce
and it is being set to an initial value of 0
at the end of the reduce
method so that it can be added to the current value num
and accumulated as it moves along the from one number to the other in the array.
Example 2
Apply reduce and add "-" at the end of every city in the array.
const cities = ["Lagos", "Paris", "Miami", "Mumbai" ]
Solution
const dashCities = cities.reduce((result, city)=> result + city + "-", "")
console.log(dashCities)
//output is Lagos-Paris-Miami-Mumbai-
Here we can see that the cities are brought together with dashes after them and made into a string because result
which is a parameter and the accumulator has an initial value that is set to an empty string at the end of the reduce
method.
I hope you enjoyed the explanation and now understand how reduce
works now. Please like, share, comment and follow for more.
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