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Functional Programming from Four Semesters of Computer Science in 5 Hours by Brian Holt
Posted on August 27, 2020 in Algorithms, JavaScript by Matt Jennings

Functional Programming Concepts

  1. Avoid side effects, or keep functions pure.
  2. Use Higher-Order Functions, which are functions that receives a function an as argument or returns the function at output.
  3. Higher-Order Functions can be used on lists (or arrays) to transform lists of data. Function calls can be chained together to describe what we want to happen, rather than how.

.reduce() for Arrays

Example code:

const addTogether = list => {
  return list.reduce((acc, num) => acc+num, 0);
};

const testList = [5,3,0,7,2,5,6,10,9]
console.log(addTogether(testList)); // 47


const concatenateStringsWithSpaces = list => {
  return list.reduce((acc, string) => acc + string + " ", "");
};

const testList = ['this', 'is', 'so', 'fun'];
console.log(concatenateStringsWithSpaces(testList).trim()); // 'this is so fun')


const squaresAndSubtracts = list => {
  return list
    .map( num => num*num )
    .reduce( (accumulator, num) => accumulator - num );
};

const testList = [10, 5, 4, 2, 1];
console.log(squaresAndSubtracts(testList)); // 54

.filter() for Arrays

const filterOutOdds = nums => nums.filter( num => num % 2 === 0);

const list = [1,5,7,2,6,3,5,4,10,50,51];
console.log(filterOutOdds(list)); // [2,6,4,10,50]

 

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