JavaScript Higher Order Functions & Arrays

In this, we will look at some of the very powerful higher-order functions and working with arrays. We will look at forEach, map, filter, reduce and sort.

ref-https://jsfiddle.net/bradtraversy/e5rb0x0a/

const companies= [

  {name: "Company One", category: "Finance", start: 1981, end: 2004},

  {name: "Company Two", category: "Retail", start: 1992, end: 2008},

  {name: "Company Three", category: "Auto", start: 1999, end: 2007},

  {name: "Company Four", category: "Retail", start: 1989, end: 2010},

  {name: "Company Five", category: "Technology", start: 2009, end: 2014},

  {name: "Company Six", category: "Finance", start: 1987, end: 2010},

  {name: "Company Seven", category: "Auto", start: 1986, end: 1996},

  {name: "Company Eight", category: "Technology", start: 2011, end: 2016},

  {name: "Company Nine", category: "Retail", start: 1981, end: 1989}

];

const ages = [33, 12, 20, 16, 5, 54, 21, 44, 61, 13, 15, 45, 25, 64, 32];

for(let i = 0; i < companies.length; i++) {

   console.log(companies[i]);

}

// forEach

companies.forEach(function(company) {

   console.log(company.name);

});

// filter

// Get 21 and older

let canDrink = [];

for(let i = 0; i < ages.length; i++) {

 if(ages[i] >= 21) {

   canDrink.push(ages[i]);

   }

}

const canDrink = ages.filter(function(age) {

   if(age >= 21) {

     return true;

   }

});

const canDrink = ages.filter(age => age >= 21);

// Filter retail companies

const retailCompanies = companies.filter(function(company) {

   if(company.category === 'Retail') {

     return true;

   }

});

const retailCompanies = companies.filter(company => company.category === 'Retail');

// Get 80s companies

const eightiesCompanies = companies.filter(company => (company.start >= 1980 && company.start < 1990));

// Get companies that lasted 10 years or more

const lastedTenYears = companies.filter(company => (company.end - company.start >= 10));

// map

// Create array of company names

const companyNames = companies.map(function(company) {

   return company.name;

});

const testMap = companies.map(function(company) {

   return `${company.name} [${company.start} - ${company.end}]`;

});

const testMap = companies.map(company => `${company.name} [${company.start} - ${company.end}]`);

const ageMap = ages

   .map(age => Math.sqrt(age))

   .map(age => age * 2);

// sort

// Sort companies by start year

const sortedCompanies  = companies.sort(function(c1, c2) {

   if(c1.start > c2.start) {

     return 1;

   } else {

     return -1;

   }

});

const sortedCompanies = companies.sort((a, b) => (a.start > b.start ? 1 : -1));

// Sort ages

const sortAges = ages.sort((a, b) => a - b);

console.log(sortAges);

// reduce

let ageSum = 0;

for(let i = 0; i < ages.length; i++) {

   ageSum += ages[i];

}

const ageSum = ages.reduce(function(total, age) {

   return total + age;

}, 0);

const ageSum = ages.reduce((total, age) => total + age, 0);

// Get total years for all companies

const totalYears = companies.reduce(function(total, company) {

   return total + (company.end - company.start);

}, 0);

const totalYears = companies.reduce((total, company) => total + (company.end - company.start), 0);

// Combine Methods

const combined = ages

  .map(age => age * 2)

  .filter(age => age >= 40)

  .sort((a, b) => a - b)

  .reduce((a, b) => a + b, 0);

console.log(combined);