CODEWITHSUNDEEP
javascriptreduce
Rob
Rob

Reputation: 33

Passing a parameter into a reducer function

I'm learning how to utilize reduce but still have a little bit of a mental block on the acc, val parameters. My goal is to be able to pass additional parameters into a reducer function and feel pretty certain that I am just going about it the wrong way.

const array = [1,2,3,4,5];

const multiply = (num, multiplier) => num * multiplier;

const multiplier = (acc, val) => acc += multiply(val, 4);

const result = array.reduce(multiplier);

console.log(result);

In this code block, I'm running the multiplier reducer against my array to multiple each value by 4. This code works correctly and is all well and good, but I want to make it so that any value can be passed in instead of the hard coded 4. I've tried things like

const multiplier = (acc, val, multiple) => acc += multiply(val, multiple);
const result = array.reduce(multiplier(4)

to be able to pass in a multiplier but the "acc, val" params are messing me up because I don't specifically "see" what the values are that are passed in. I know that it passes in 1 then 2 then 3 etc. but how do you pass an additional parameter in such as a custom multiplier instead of needing a different multiplier function for every multiple?

Upvotes: 3

Views: 530

Answers (1)

buzatto
buzatto

Reputation: 10382

do it as a currying function that will work as expected:

const multiplier = factor => (acc, val) => acc += multiply(val, factor);
const result = array.reduce(multiplier(4));

This way when you call multiplier(4) it will return a function tailored with the desired factor that you can use at your reducer like you intended to.

Upvotes: 1

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