js数组方法

 indexOf

数组可以通过indexOf()来搜索一个指定的元素的位置，如未找到返回 -1；
var arr = [10,20,"30","abc"];
console.log(arr.indexOf(10)); //元素10的索引为0

concat

concat()方法把当前的  数组  和  另一个  数组连接起来，并返回一个新的  数组；
var arr1 = ["a","b","c"];
var arr2 = [1,2,3];
var newArr = arr1.concat(arr2,"再次添加");
newArr; //["a","b","c",1,2,3,"再次添加"];

 push和pop

push()向数组的末尾添加若干元素，pop()  则把  数组的最后一个元素删除掉
var arr = [1,2];
arr.push("a","b");
console.log(arr);//[1,2,"a","b"]

arr.pop(); //pop() 返回“b”;
arr; //打印[1,2,"a"]

unshift和shift

unshift()  向数组前面添加若干元素，shift()  则把数组的第一个元素删除掉
var arr = [1,2];
arr.unshift("a","b"); //返回新长度 4
arr;//打印["a","b",1,2]
arr.shift();//返回"a"
arr; //打印["b",1,2]

slice

slice()  截取数组的部分元素，然后返回一个新的数组
var arr = ["a","b","c","d","e","f","g"];
console.log(arr.slice(0,3)); //从索引0开始，到索引3结束，但不包括3：["a","b","c"]
console.log(arr.slice(3));  //从索引3开始到结束："d","e","f","g"

join

join()  方法把数组的每个元素用指定的字符串连接起来，然后新的字符串

var arr = ["a","b","c",1,2,3]; arr.join("-");  //"a-b-c-1-2-3"

splice
splice() 方法是修改数组的“万能方法”，他可以从指定的索引开始删除若干元素，然后再从该位置添加若干元素；
var arr = ["苹果","橘子","香蕉","芋头","桂圆","山楂"];

//从索引2开始删除3个元素，然后再添加两个元素
arr.splice(2,3,"白梨","西瓜");
console.log(arr); // "苹果","橘子","白梨","西瓜","山楂"