freecodecamp JavaScript学习(三)

1. Make Object Properties Private
   -var 定义私有属性，方法， this定义公共属性，方法

var Car = function() {  // this is a private variable  var speed = 10;  // these are public methods  this.accelerate = function(change) {    speed += change;  };  this.decelerate = function() {    speed -= 5;  };  this.getSpeed = function() {    return speed;  };};

2.Iterate over Arrays with map
-map函数迭代数组中的每个元素，并且有一个回调函数可以改变数组中的每个值，并且将改变的数组生成一个新的数组，并不影响原有的数组

var oldArray = [1,2,3,4,5];// Only change code below this line.var newArray = oldArray.map(function(val,index){  if((index%2)===0){    //the odd plus 3     return val+3;  }else    //the even plus 5  {    return val+5;  }});

var oldArray = [1, 2, 3];var timesFour = oldArray.map(function(val){  return val * 4;});console.log(timesFour); // returns [4, 8, 12]console.log(oldArray);  // returns [1, 2, 3]

3.Condense arrays with reduce
MDN上的解释：reduce

• arr.reduce(callback, [initialValue])

[0, 1, 2, 3, 4].reduce(  (accumulator, currentValue, currentIndex, array) => {    return accumulator + currentValue;  },  10);

var sum = [0, 1, 2, 3].reduce(function (a, b) {  return a + b;});// sum is 6,无初始值，第一次调用时，acc=0,cur=1,即从第二个值开始

var total = [ 0, 1, 2, 3 ].reduce(  ( acc, cur ) => acc + cur,  10);// sum is 16 with initial value 10, 第一次调用时，acc=10,cur=0，有设初始值时，从数组第一个值开始

4.Filter Arrays with filter
-过滤数组

array = array.filter(function(val) {  return val !== 5;});//将5从数组中清除，并不改变原有数组，产生一个新的数组

5.Sort Arrays with sort
MDN上sort的内容

arr.sort()arr.sort(compareFunction)

-sort直接改变原有数组
-compareFunction(a,b), 当返回值大于0，则a在b的后面；当返回值<0,则a在b的前面
-当没有compareFunction时，按字符串格式比较大小，数字，大写字母，小写字母排序

6.Reverse Arrays with reverse
-将产生一个新的数组，并将改变原来的数组

var myArray = [1, 2, 3];myArray.reverse();//[3，2，1]

7.Concatenate Arrays with concat
-将一个数组直接和另一个数组连接，产生一个新的数组

var oldArray = [1,2,3];var newArray = [];var concatMe = [4,5,6];newArray = oldArray.concat(concatMe);//[1,2,3,4,5,6,]

8.Split Strings with split

var string = "Split me into an array";var array = [];array = string.split(' ');//['Split','me','nto','an','array']

9.Join Strings with join

var joinMe = ["Split","me","into","an","array"];var joinedString = '';joinedString = joinMe.join(' ');// "Split me into an array"