js数组(列表)的基本操作

unshift()
var a = [1,2.5,"a","yes"];
var temp = a.unshift(-1,-2.2);
console.log(a);     //[-1, -2.2, 1, 2.5, "a", "yes"]
console.log(temp);  //6 数组的长度

push()
var a = [1,2.5,"a","yes"];
var temp = a.push(-1,-2.2);
console.log(a);     //[1, 2.5, "a", "yes", -1, -2.2]
console.log(temp);  //6 数组的长度
  
splice()    将数据添加到原数组结尾
var a = [1,2.5,"a","yes"];
var temp = a.splice(a.length,0, -1,-2.2);    //此将数据添加到原数组结尾，同push()
console.log(a);     //a: [1, 2.5, "a", "yes", -1, -2.2]
console.log(temp);  //[] 空数组

splice()    将数据添加到原数组开头
var a = [1,2.5,"a","yes"];
var temp = a.splice(0,0, -1,-2.2);   //此将数据添加到原数组开头，同unshift()
console.log(a);     //a: [-1, -2.2, 1, 2.5, "a", "yes"]
console.log(temp);  //[] 空数组

splice()    将数据添加到具体位置
var a = [1,2.5,"a","yes"];
var temp = a.splice(2,0, -1,-2.2);   //此将数据添加到第三个位置
console.log(a);     //a: [1, 2.5, -1, -2.2, "a", "yes"]
console.log(temp);  //[] 空数组

shift()
var a = [1,2.5,"a","yes"];
var temp = a.shift();
console.log(a); //[2.5, "a", "yes"]
console.log(temp);  // 1 原数组第一项
      
pop()
var a = [1,2.5,"a","yes"];
var temp = a.pop();
console.log(a); // [1, 2.5, "a"]
console.log(temp);  // yes 原数组最后一项

splice()    删除指定位置开始的数据。第一个参数是指定位置，第二个参数是删除从指定位置开始的数据个数
var a = [1,2.5,"a","yes"];
var temp = a.splice(1,1);       //删除第2个位置开始的1个数据，
console.log(a); // [1, "a", "yes"]
console.log(temp);  // [2.5] 以数组形式返回移除的元素

var temp = a.splice(1,2);       //删除第2个位置开始的2个数据，
console.log(a); // [1, "yes"]
console.log(temp);  // [2.5, "a"] 以数组形式返回移除的元素

var a = [1,2.5,"a","yes"];
a[2] = "IT";
console.log(a); // [1, 2.5, "IT", "yes"]

var a = [1,2.5,10,"No","a","yes"];      通过指定位置先删除再插入，达到修改数组的目的
var temp = a.splice(2,2,"You",0.1);
console.log(a);     // [1, 2.5, "You", 0.1, "a", "yes"]
console.log(temp);  // [10, "No"] 其实就是删除项，用数组形式返回

var a = [1,2.5,"a","yes"];
var temp = a[1];
console.log(temp);  // 2.5 返回数组索引为1的元素值
var temp = a[1,2]; var temp = a[-1];　　//这两种都是错误的，无法获取想要的数据

var a = [1,5,2,15,6];
var b = ["You","No","a","yes"];
var temp = a.concat(b); //将b合并到a后面
var tempdata = b.concat(a);     //将a合并到b后面
console.log(temp);      // [1, 5, 2, 15, 6, "You", "No", "a", "yes"]
console.log(tempdata);     //["You", "No", "a", "yes", 1, 5, 2, 15, 6]

var a = [1,5,2,15,6];
var b = ["You","No","a","yes"];
for(var i=0; i.length; i++){
 a.push(b[i])        //将b加在a后面；如果希望将b加在a前面，则改用unshift（）
}
console.log(a); // [1, 5, 2, 15, 6, "You", "No", "a", "yes"]
console.log(b);  // ["You", "No", "a", "yes"]

var a = [1,2.5,"a","yes",12,23];
var temp = a.slice(2,5); //裁剪下标为2到下标为5的元素；结束下标未超出数组总长
console.log(temp);  // ["a", "yes", 12]
console.log(a);     // [1, 2.5, "a", "yes", 12, 23] 原数组不发生改变 

var temp = a.slice(2,15);   //裁剪下标为2到下标为15的元素；结束下标超出数组总长
console.log(temp);  // ["a", "yes", 12, 23] 结束下标自动以原数组结尾下标为结束下标
console.log(a);     // [1, 2.5, "a", "yes", 12, 23]

1、纯字符串排序
var a = ["zhao","qian","sun","li","zhou","wu","zheng"];
var temp = a.sort();
console.log(a); // ["li", "qian", "sun", "wu", "zhao", "zheng", "zhou"]
console.log(temp);  // ["li", "qian", "sun", "wu", "zhao", "zheng", "zhou"] 返回排好序的原数组 先按第一个字母排序，第一个相同则按第二个排序，以此类推。

2、字符串和数字混杂
var a = ["zhao","qian",1,"li","zhou","wu",2];
var temp = a.sort();
console.log(a); //[1, 2, "li", "qian", "wu", "zhao", "zhou"] 
先排数字，后排字符串，其实这的1,2排序看似正确，其实不是按照他们的大小排的，而是按照1和2的编码顺序排的。从下面这个例子可以看出。

3、  纯数字排序(但不提供比较函数)
var a = [11,5,1,13,20,-1,2];
var temp = a.sort();
console.log(a);  // [-1, 1, 11, 13, 2, 20, 5] 
从这就可以看出默认排序是按照字符编码顺序排的，而不是大小

4、  纯数字正确排序(需要提供排序函数)
var a = [11,5,1,13,20,-1,2];
var temp = a.sort(sortNumber);
console.log(a);  // [-1, 1, 2, 5, 11, 13, 20] 这才是正确的从小到大排序
function sortNumber(a,b) 这是从小到大排序{
    return a - b
}
function sortNumber(a,b) 这是从大到小排序
{
    return b – a
}
console.log(a);  // [20, 13, 11, 5, 2, 1, -1] 这是从大到小排序结果    

var a = [1,2.5,"a","yes",12,23];
var temp = a.join();  //默认格式化，不提供连接字符
console.log(temp); //1,2.5,a,yes,12,23
console.log(a);　　// [1, 2.5, "a", "yes", 12, 23]

var a = [1,2.5,"a","yes",12,23];
var temp = a.join(“|”);   //提供连接字符,但连接字符必须是字符(“x”)形式
console.log(temp); // 1|2.5|a|yes|12|23
console.log(a);　　// [1, 2.5, "a", "yes", 12, 23]