Codecademy export

main.js

//challenge 1: define a callback function before you use it an iterator
const capitals = [ 'Amsterdam', 'London', 'Brussels', 'Oslo', 'Stockholm', 'Paris', 'Ankara', 'Alberta'];

const cityA = cityA => {  //callback function
  return cityA[0] === 'A';
};

const startsWithA=capitals.filter(cityA); //iterator

console.log(startsWithA);

//challenge 2: chain two iteration methods
const shortCity=startsWithA.some(city => city.length < 7);

//challenge 3, use optional arguments in an iterator
console.log(capitals.indexOf('Brussels', 0)); //should return 2

// challenge 4: return a single array from a multilayer array
const numbers = [[1,2],[3,4],[5,6],[7,8]];

let newArray = numbers.reduce(function(accumulator, currentValue) {
    return accumulator.concat(currentValue);
  },
  []
);

console.log(newArray);