05-ArrayMethods.js

// @ts-check

//* ************** Joining multiple arrays
const zero = 0;
const positiveNumbers = [1, 2, 3];
const negativeNumbers = [-3, -2, -1];
let numbers = negativeNumbers.concat(zero, positiveNumbers);

console.log('zero', zero);
console.log('positiveNumbers', positiveNumbers);
console.log('negativeNumbers', negativeNumbers);
console.log('negativeNumbers.concat(zero, positiveNumbers)', numbers);

/* function isEven(x) {
  // returns true if x is a multiple of 2.
  console.log(x);
  return x % 2 === 0 ? true : false;
} */ // ES5 syntax
const isEven = x => x % 2 === 0;

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
console.log('numbers', numbers);

// it is going to execute the function only once
console.log('numbers.every(isEven)', numbers.every(isEven));

// is going to execute the function twice
console.log('numbers.some(isEven)', numbers.some(isEven));

/* numbers.forEach(function(x) {
  console.log(x % 2 == 0);
}); */ // ES5 sintax for function below

numbers.forEach(x => console.log(`numbers.forEach: ${x} % 2 === 0`, x % 2 === 0));


console.log('numbers.map(isEven)', numbers.map(isEven));

console.log('numbers.filter(isEven)', numbers.filter(isEven));

/* console.log('numbers.reduce',
  numbers.reduce(function(previous, current, index) {
    return previous + current;
  })
); */ // ES5 sintax for function below

console.log('numbers.reduce', numbers.reduce((previous, current) => previous + current));