//forEach迭代器
function square(num){
  document.write(num + ' ' + num*num + '<br>');
}

var nums = [1,2,3,4,5,6,7,8];
nums.forEach(square);

//every迭代器
function isEven(num){
  return num % 2 == 0;
}
var nums = [2,4,6,8];
document.write(nums.every(isEven));

//some迭代器
function isEven(num){
  return num % 2 == 0;
}
var nums = [1,3,5,7];
document.write(nums.some(isEven));

//reduce迭代器
function add(runningTotal, currentValue){
  return runningTotal + currentValue;
}
var nums = [1,2,3,4,5,6,7,8,9,10];
var sum = nums.reduce(add);
document.write(sum);

add(1,2) -> 3
add(3,3) -> 6
add(6,4) -> 10
add(10,5) -> 15
add(15,6) -> 21
add(21,7) -> 28
add(28,8) -> 36
add(36,9) -> 45
add(45,10) -> 55

//使用reduce连接数组元素
function concat(accumulatedString, item){
  return accumulatedString + item;
}
var words = ['the ', 'quick ', 'brown ', 'fox'];
var sentence = words.reduce(concat);
document.write(sentence);

//使用reduce连接数组元素
function concat(accumulatedString, item){
  return accumulatedString + item;
}
var words = ['the ', 'quick ', 'brown ', 'fox '];
var sentence = words.reduceRight(concat);
document.write(sentence);

//使用map迭代器生成新的数组
function curve(grade){
  return grade+5;
}
var grades = [77,65,81,92,83];
var newgrades = grades.map(curve);
document.write(newgrades);

function isEven(num){
  return num % 2 == 0;
}

function isOdd(num){
  return num % 2 != 0;
}

var nums = [];
for (var i=0; i<20; i++) {
  nums[i] = i+1;
}
var evens = nums.filter(isEven);
document.write(evens);
document.write('<br>');
var odds = nums.filter(isOdd);
document.write(odds);