allOrSomeEvens.js

function allEven(arr){
    // check if all are even numbers
    return arr.every(num => {
        return num%2 === 0;
    }
    );
}

// alt, check if all are even
const allEvens = (arr) => {return arr.every(num => {return num%2===0;});};

console.log(allEvens([2,4,6,8])) //true
console.log(allEvens([1,4,6,8])) //false
console.log(allEvens([1,2,3])) //false

// check if some are even 
const someEvens = arr => {return arr.some(num => {return num%2 === 0;});}
console.log(allEvens([2,4,6,8])) //true, cause [2,4,6,8]
console.log(allEvens([1,4,6,8])) //true, cause [4,6,8]
console.log(allEvens([1,2,3])) //true, cause [2]

defaultParams.js

function rollDie(sides) {
  return Math.floor(Math.random() * sides) + 1);
}

console.log(rollDie(6)) // something between 1 -> 6
console.log(rollDie()) // NaN

// old fix, 'check undefined'
function rollDieOld(sides) {
  if (sides === undefined) {
    sides = 6 ; // default sides is 6 
  }
  return Math.floor(Math.random() * sides) + 1);
}

console.log(rollDieOld(6)) // something between 1 -> 6
console.log(rollDieOld()) // something between 1 -> 6

// new fix, using default value of sides = 6
function rollDieNew(sides = 6) {
  return Math.floor(Math.random() * sides) + 1);
}

console.log(rollDieOld(6)) // something between 1 -> 6
console.log(rollDieOld()) // something between 1 -> 6


// also
function greet(salutation="Hello", name="World"){
  return `${salutation} ${name}`;
}

console.log(greet("Afternoon","Traveller")); // "Afternoon Traveller"
console.log(greet()); // "Hello World"

javascriptMethods.js

// functions inside objects are called methods
const square = {
    area : function(side){
        return side * side;
    },
    perimeter(side){
        return side * 4;
    }
}

console.log(square.area(10)) //100
console.log(square.perimeter(10)) //40

mapPractice.js

// DO NOT ALTER THE FOLLOWING CODE:
const fullNames = [{first: 'Albus', last: 'Dumbledore'}, {first: 'Harry', last: 'Potter'}, {first: 'Hermione', last: 'Granger'}, {first: 'Ron', last: 'Weasley'}, {first: 'Rubeus', last: 'Hagrid'}, {first: 'Minerva', last: 'McGonagall'}, {first: 'Severus', last: 'Snape'}];

// Write your code here

let firstNames = fullNames.map(function(fullName){
   return fullName.first; 
});

console.log(firstNames); //  ['Albus', 'Harry', 'Hermione', 'Ron', 'Rubeus', 'Minerva', 'Severus']

validUsernames.js

function validUserNames(usernames) {
  // get usernames with less than 10 characters
  return usernames.filter((username) => username.length < 10 );
}

console.log(validUserNames(['mark', 'staceysmom1978', 'q29832128238983', 'carrie98', 'MoanaFan']));

// or

const validUserNamesAlt = usernames => {
    return usernames.filter((username) => username.length < 10 );
};

console.log(validUserNamesAlt(['mark', 'staceysmom1978', 'q29832128238983', 'carrie98', 'MoanaFan']));