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June 22, 2021 11:25 pm GMT

Day 7 of 100DaysOfCode!

Today's progress

Today I learned about functional programming.

What I learned

Functional programming is a style of programming in which solutions are simple. A function takes an input, processes it and returns an output.

Three important factors of functional programming:

  • Isolated function - does not depend on outside variables (global variables)
  • Pure functions - same input always give the same output
  • Function has limited side effects - this means any changes or mutations is controlled.

This allows for greater control, less mutation or changing of variables and objects.

For instance, let's say we have a global variable called animals and stores an array of different animals.

let animals = ['lion', 'eagle', 'cheetah', 'bear', 'giraffe']

Let's create two functions. One function adds a new animal and the other function removes an animal.

// adds an animal to arrfunction add(arr, animalName){    // make a copy of the array of animals    let newArr = [...arr]    // push new animal to new arr    newArr.push(animalName);    // return the new array    return newArr;}// removes an animal from arrfunction remove(arr, animalName){    //make a copy of the array of animals    let newArr = [...arr]    // grab the index of the animal name    // store into variable    animal_index = newArr.indexOf(animalName)    // if the animal's index exist    // remove it, use splice    if(animal_index >= 0){        newArr.splice(0, 1)    }    // return the new array    return newArr;}

You'll notice in the above code that we created two functions and in both functions take two parameters. The first parameter is the array and the second parameter takes in a string animal.

Inside the functions we added a line of code that makes a copy of the global array by passing it through our function argument function add(arr, animalName) and function remove(arr, animalName)

let newArr = [...arr]

Now, when I test this using the functions above. I will get one function that adds a new animal and the other function that removes an animal from the array all without mutation the original array.

function add(arr, animalName)

let addAnimal = add(animal, 'monkey')console.log(addAnimal)//output: ['lion', 'eagle', 'cheetah', 'bear', 'giraffe', 'monkey']

function remove(arr, animalName)

let removedAnimal = remove(animal, 'lion')console.log(removedAnimal)//output: ['eagle', 'cheetah', 'bear', 'giraffe']

When I run a console.log on the global variable animals from earlier. The global variable did not change at all.

let animals = ['lion', 'eagle', 'cheetah', 'bear', 'giraffe']console.log(animals)//output: ['lion', 'eagle', 'cheetah', 'bear', 'giraffe']

This is the benefit of using functional programming as a way to copy the global variable within the scope of the function. Then from there can mutate or change it without affecting the global variable and thus returning a new copy of the variable or object.


Original Link: https://dev.to/cfalucho/day-7-of-100daysofcode-2ek7

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