数组API
1.String();把数组转化为字符串
var a=[1,2,3,4,5];
var str=String(a);
console.log(str);1,2,3,4,5
2.join('拼接符')；拼接，最后拼接成字符串；如果没有拼接符，默认等于string;
var a=['h','e','l','l','o'];
var str=a.join('-');h-e-l-l-o
var str=a.join('');hello
var str=a.join();h,e,l,l,o
console.log(str);
3.concat();拼接 结果还为数组
var arr=['a','b','c'];
var arr2=[1,2,3];
var str=arr.concat(arr2);['a','b','c',1,2,3]
var str=arr.concat(1,2);['a','b','c',1,2]
console.log(str);
console.log(typeof str);//object
4.slice(starti,endi);截取
1).含头不含尾
2).如果省略第二个参数，默认从starti开始截取到结尾
3).如果参数一个都不写，相当于复制原数组
4).支持负数参数
var arr=['a','b','c','d','e','f'];
// 0 1 2 3 4 5
// -6 -5 -4 -3 -2 -1
var str=arr.slice(2,5);//['c','d','e']
var str=arr.slice(2);//['c','d','e','f']
var str=arr.slice();//['a','b','c','d','e','f']
var str=arr.slice(-4,-2);['c','d']
console.log(str);
5.splice(starti,n);删除插入替换
var arr=['a','b','c','d','e','f'];
// 0 1 2 3 4 5
删除：
var str=arr.splice(3,2);//['a','b','c','f']
插入：
var str2=arr.splice(3,0,'1','2');//['a','b','c','1','2','d','e','f']
替换：
var str3=arr.splice(3,2,'A','B');//['a','b','c','A','B','e','f']
console.log(arr);
6.reverse();翻转
var arr=[1,2,3,4,5];
var str=arr.reverse();
console.log(str);[5,4,3,2,1]
7.push();给数组末尾添加元素
var arr=[1,2,3,4,5];
var str=arr.push('a');
console.log(arr);[1,2,3,4,5,'a']
8.pop();删除数组末尾的元素
var arr=[1,2,3,4,5];
var str=arr.pop();
console.log(arr);[1,2,3,4]
9.unshift();给数组开头添加一个元素
var arr=[1,2,3,4,5];
var str=arr.unshift('520');
console.log(arr);['520',1,2,3,4,5]
10.shift();删除开头第一个元素
var arr=[1,2,3,4,5];
var str=arr.shift();
console.log(arr);[2,3,4,5]
