var arr = [1, 2, 3];

arr.forEach(function(item,index) {
  console.log(item,index);
});

// expected output: 1 0
// expected output: 2 1 
// expected output: 3 2

var arr = [1, 2, 3];
var arr2 = arr.map(function(item,index){
    return '<b>'+item+'</b>';

})
console.log(arr2); 
// expected output: ["<b>1</b>", "<b>2</b>", "<b>3</b>"]

var arr = [1, 2, 3];
var arr2 = arr.filter(function(item,index){
    if(item>2) {
        return true;
    }
})
console.log(arr2); 
// expected output: [3]

var arr = [1, 2, 3];
var found = arr.find(function(item,index){
    return item>1;
})
console.log(found);
// expected output: 2

var arr = [1, 4, 2, 3, 5];
var arr2 = arr.sort(function(a,b){
    return a - b; //從小到大排序
    //return b - a; //從大到小排序
})
console.log(arr2); 
// expected output: [1, 2, 3, 4, 5]

var arr = [1, 2, 3];
var result = arr.every(function(item,index){
  if(item<4) {
    return true;
  }
})
console.log(result);
// expected output: true

var arr = [1, 2, 3];
var result = arr.some(function(item,index){
  if(item<2) {
    return true;
  }
})
console.log(result);
// expected output: true

const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));
// expected output: 10

var arr = ["vue", "raact","JavaScript", "Angular", "jQuery"];
var longest = arr.reduce((a, b) => a.length > b.length ? a : b, '');
console.log(longest); //  "JavaScript"

let arr = [
  { product:'The Godfather', catalog:'movie',price:'150'},
  { product:'The Dark Knight', catalog:'movie',price:'100'},
  { product:'7 Rings', catalog:'music',price:'300'}
]

var arrFilter = arr.filter(function(item,index){
    if(item.catalog =="movie") {
      return true;
    }
})
console.log(arrFilter); //arr catalog:'music'

var arrSortPrice = arr.sort(function(a,b) {
    return b.price - a.price;
})
console.log(arrSortPrice); // arr 300 150 100  

let sum = 0;
arr.forEach(function(element) {
    sum+=parseInt(element.price);
});

console.log(sum); //sum price 550

const arr = [1, 2, 3, 4, 5];
const arr1 = arr.map(num => num * 2).filter(num => num > 5);
console.log(arr); // [1, 2, 3, 4, 5]
console.log(arr1); // [6, 8, 10]