Our pipeline will consist of our three functions in the order that we want to use them. We don’t want to have to rewrite our function every time so we going to use reduce to create a pipeline.Ī pipeline is a term used for a list of functions that transform some initial value into a final value. The problem is that we know we are going to need to increment the amount three times, then double it, then decrement it, and then halve it at some point in the future.

You could write a function that takes an input, and returns (input + 1) * 2 -1. Var sum = euros.reduce( function(total, amount)įor whatever reason, we need to increment, then double, then decrement an amount. It’s exactly the same as writing: var euros = If you have never used ES6 syntax before, don’t let the example above intimidate you. The ES5 version of the Reduce Method In JavaScript When there are no more numbers left in the array the method returns the total value.The calculation is repeated for each amount in the array, but each time the current value changes to the next number in the array, moving right.In this particular example, we want to add the current amount to the total.When the loop starts the total value is the number on the far left (29.76) and the current amount is the one next to it (41.85).The reduce method cycles through each number in the array much like it would in a for-loop.

In this example, Reduce accepts two parameters, the total and the current amount.

const euros = Ĭonst sum = euros.reduce((total, amount) => total + amount) Use it when: You have an array of amounts and you want to add them all up. Let’s explore how it works, when you should use it, and some of the cool things it can do. JavaScript’s reduce method is one of the cornerstones of functional programming. By Josh Pitzalis How JavaScript’s Reduce method works, when to use it, and some of the cool things it can do Image credit to Karthik Srinivas.

What does reduce do in javascript