JavaScript数组多种方法以及字符串方法的功能你了解多少??（学了多种语言后，你会发现他们都是有很多共同之处的）

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
console.log(arr.indexOf(30)); //元素30未找到，返回-1
//注意：数字30和字符串"30"是不同元素

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"];
arr1; //["a","b","c"]

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"]
arr.pop();arr.pop();arr.pop(); //连续3次pop
arr; //打印[]
arr.pop(); //空数组继续pop不会报错，而是返回undefined
arr;//打印[]

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]
arr.shift();arr.shift();arr.shift(); //连续3次
arr; //打印[]
arr.shift(); //空数组继续删除不报错，返回undefined
arr; //打印[]

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"

如果不给slice()传递任何参数，他就会从头到尾截取所有元素。利用这一点，可以很容易的复制一份新的数组

var arr = [1,2,3];
var aCopy = arr.slice();
aCopy; //[1,2,3]

sort

sort() 可以对当前数组排序

var arr = ["b","c","a"];
arr.sort();
arr;//["a","b","c"]

reverse

reverse() 把整个数组的元素给掉个个，也就是反转

var arr = ["one","two","three"];
arr.reverse();8
arr; //["three","two","one"]

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；

//splice(索引值，删除数量，"值1"，"值2");
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"
//只删除，不添加
arr.splice(2,2); //"白梨","西瓜"
console.log(arr); //"苹果","橘子","山楂"
//只添加，不删除
arr.splice(2,0,"白梨","西瓜");
console.log(arr);// "苹果","橘子","白梨","西瓜","山楂"

字符串的方法

slice()

slice(start[,end])，start--开始索引 end--结束索引

var str = "中华人民共和国";
var str1 = str.slice(2,4); //人民

substr()

substr(start[,length])，start：开始，取length个字符

var str = "中华人民共和国";
var str1 = str.substr(2,5); //人民共和国

split()

split([separator[,limit]])，按条件分割字符串，返回数组

var str = "中华人民共和国";
var arr = str.split(""); //["中", "华", "人", "民", "共", "和","国"]
var str1 = "杏|石|口|路|81|号";
var arr1 = str1.split("|"); //["杏", "石", "口", "路", "81", "号"]

indexOf()

在父串中首次出现的位置，从0开始！没有返回-1

lastIndexOf()

倒序查找

charAt(index)

charAt(index) 指定索引的字符

toLowerCase()

转小写

toUpperCase()

转大写