ReduceInJS

ReduceInJS.js

// Here we have a list of all the transactions made by Mike
const transActionsForMike = [ {Name: "Bike", Cost: 5000}, 
                              {Name: "Apple Music", Cost: 20}, 
                              {Name: "Cook Book", Cost: 30},
                              {Name: "Azure Hosting", Cost: 60}, 
                              {Name: "Phone Bill", Cost: 70}];
                              
// And we try to figure out how much Mike Spent
// "reduce" takes in three main arguments, the Accumulator (acc), the 
// currentValue (curr) in the form of an anonymous function. And a inital 
// value for the accumulator (in our example its 0). The accumulator acts
// like a bucket that you keep adding things to. Or keep modifying every 
// interaction of the reduce function.

// Here we are taking each object in the "transActionsForMike" variable. Then
// we are accessing the cost property of each object, then continuously adding it to 
// the accumulator.

// then at the very end we are returning the accumulator that gets dumped into the 
// MikesSpending variable.
let MikesSpending = transActionsForMike.reduce((acc, curr) =>{
    return acc + curr.Cost;
}, 0);

console.log(MikesSpending) // MikesSpending is: 5180

// Note you can make the accumulator into anything you want. That is, you can set the 
// inital property of the accumulator to object or array and continously add things 
// to it, to have the desired output.

// Other things that you can have "reduce" pass into your function is:
// accumulator, currentValue, currentIndex, array (yes the whole array)