JS基础--Array

value instanceof Array;
Array.isArray(value);//value 为数组

var arr=["arr1","arr2","arr3"];
console.log(arr.toString());//arr1,arr2,arr3
console.log(arr.toLocaleString());//arr1,arr2,arr3
console.log(arr.valueOf());//["arr1", "arr2", "arr3"]，可以通过这种方式将一个数组赋值给另一个数组,若对这个数组操作，会对原数组有一样的操作。
console.log(arr);//["arr1", "arr2", "arr3"]
console.log(arr.join("||"));//arr1||arr2||arr3 返回字符串，对原数组没有改变
//若某一项为null或者为undefined时，那么在join(),toLocaleString(),toString()中以空字符串表示

var arr=["arr1"];
var count=arr.push("arr2","arr3");//返回修改后数组长度
console.log(count);//3
console.log(arr);//["arr1","arr2","arr3"]
var theTop=arr.pop();//返回取出的元素，从arr[arr.length-1]开始取
console.log(theTop);//arr3字符串
console.log(arr);//["arr1","arr2"]

var arr=[];
var count=arr.push("arr1","arr2");//返回修改后数组长度
console.log(count);//2
console.log(arr);//["arr1","arr2"]
var theBottom=arr.shift();//返回取出的元素,从arr[0]开始取
console.log(theBottom);//arr1字符串
console.log(arr);//["arr2"]
var count=arr.unshift("arr1","arr0");//在前面增加，增加arr[0]
console.log(count);//3，返回修改后的长度
console.log(arr);//["arr1", "arr0", "arr2"]

//reverse逆向输出
var arr=[0,1,5,10,15];
arr.reverse();//逆向输出
console.log(arr);//[15, 10, 5, 1, 0]
//sort升序排序
arr.sort();//升序排序，比较的是字符串
console.log(arr);//[0, 1, 10, 15, 5]
//sort解决方案
arr.sort(function(a,b){
  return b-a});//b-a从大到小，a-b从小到大
console.log(arr);//[15, 10, 5, 1, 0]

//concat连接
var arr=["arr1","arr2"];
var arrs=arr.concat("arr3",["arr4","arr5"]);//不影响原数组
console.log(arr);//["arr1", "arr2"]
console.log(arrs);//["arr1", "arr2", "arr3", "arr4", "arr5"]
//slice复制新数组
var arrs1=arrs.slice(1);//不影响原数组
var arrs2=arrs.slice(1,4);//不影响原数组,相当于arrs.slice(-4,-1)，负数加上数组长度再进行获取新数组
console.log(arrs1);//["arr2", "arr3", "arr4", "arr5"]，不影响原数组
console.log(arrs2);//["arr2", "arr3", "arr4"]
//splice删除
var removed=arr.splice(0,1,"arr1_1","arr1_2");//在0的位置开始删除1项，插入2项
console.log(arr); //["arr1_1", "arr1_2", "arr2"]
console.log(removed);//["arr1"]返回删除的项组成的数组

//indexOf从前往后查找
var arr=[1,2,3,4,5,4,3,2,1];
console.log(arr.indexOf(4));//3,返回4所在位置
console.log(arr.indexOf("4"));//-1，未找到的情况下为-1，按===查找
//lastIndexOf从尾部查找
console.log(arr.lastIndexOf(4));//5,返回4所在位置
console.log(arr.lastIndexOf("4"));//-1，未找到的情况下为-1，按===查找
var person={name:"XXX"};//对象
var people=[{name:"XXX"}];//数组，含一项，这一项是一个对象（跟person无关）
var morePeople=[person];//数组，含一项，这一项是一个person对象
console.log(people.indexOf(person));//-1,people数组中不含person对象
console.log(morePeople.indexOf(person));//0,morePeople数组中含person对象，为第一项

var numbers=[1,2,3,4,5,4,3,2,1];

//every,每一项都满足则返回true，否则返回false
var everyResult=numbers.every(function(item,index,array){
  return (item>2);
});
console.log(everyResult);//false

//filter，返回满足条件的项组成的数组，对原数组没有影响
var filterResult=numbers.filter(function(item,index,array){
  return (item>2);
});
console.log(filterResult);//[3, 4, 5, 4, 3]
console.log(numbers);//[1,2,3,4,5,4,3,2,1]

//forEach，相当于for循环
numbers.forEach(function(item,index,array){
  //执行某些操作
});//

//map，对数组进行操作，对原数组没有影响
var mapResult=numbers.map(function(item,index,array){
  return (item*2);
});
console.log(mapResult);// [2, 4, 6, 8, 10, 8, 6, 4, 2]
console.log(numbers);//[1,2,3,4,5,4,3,2,1]

//some，至少一项满足则返回true，否则返回false
var someResult=numbers.some(function(item,index,array){
  return (item>2);
});
console.log(someResult);//true

var numbers=[1,2,3,4,5];
//reduce,第一遍prev=1,cur=2（第二项）,第二遍prev=3（1+2）,cur=3(第三项)
var sum=numbers.reduce(function(prev,cur,index,array){
  return prev+cur;
});
console.log(sum);//15

//reduceRight,第一遍prev=5,cur=4（第四项）,第二遍prev=9（5+4）,cur=3(第三项)
var sum=numbers.reduce(function(prev,cur,index,array){
  return prev+cur;
});
console.log(sum);//15
//reduce,和reduceRight遍历方向不同，除此之外都相同